I 363 
14 
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FACTORS INFLUENCING THE ABSCISSION OF 

FLOWERS AND PARTIALLY DEVELOPED FRUITS 

OF THE APPLE (PYRUS MALUS L.) 



A THESIS 



PRESENTED TO 

THE FACULTY OF THE GRADUATE SCHOOL OF CORNELL UNIVERSITY 

FOR THE DEGREE OF DOCTOR OF PHILOSOPHY 



BY 
ARTHUR JOHN HEINICKE 



PUBLISHED AS CORNELL UNIVERSITY AGRICULTURAL 
EXPERIMENT STATION BULLETIN 393. JULY, 1917 



FACTORS INFLUENCING THE ABSCISSION OF 

FLOWERS AND PARTIALLY DEVELOPED FRUITS 

OF THE APPLE (PYRUS MALUS L.) 



A THESIS 



PRESENTED TO 

THE FACULTY OF THE GRADUATE SCHOOL OF CORNELL UNIVERSITY 

FOR THE DEGREE OF DOCTOR OF PHILOSOPHY 



BY 
ARTHUR JOHN HEINICKE 



PUBLISHED AS CORNELL UNIVERSITY AGRICULTURAL 
EXPERIMENT STATION BULLETIN 393, JULY, 1917 



6^ 









CONTENTS 

PAGE 

Survey of literature 46 

Material used in these experiments 50 

Magnitude of the first and of the June drop 50 

Flowers developing into fruits after the first drop 51 

Spurs setting fruit after the first drop 52 

Variations in percentage of spurs setting fruit after the first drop 53 

Flowers developing into fruits after the June drop 54 

Totals of flowers on many limbs 54 

Flowers falling at the first drop and at the June drop on fruit-bearing 

spurs 55 

Spurs setting fruit after the June drop 56 

Consideration of spurs from many limbs 56 

Variations in percentage of spurs setting fruit after the June drop 56 

Relation between amount of bloom and set of fruit 58 

Set of fruit on limbs with large leaves and on limbs with small leaves 58 

Set of fruit as influenced by the location of the spur on the twig growth of different 

years 59 

Set of fruit on spurs formed on different parts of a given year's growth 62 

Relation between number of flowers to the spur, and ability of the spur to set fruit . . 63 

Average number of flowers on spurs holding fruit for varying lengths of time . . 63 

Set of fruit on spurs with varying numbers of flowers 64 

Percentage of flowers developing into fruits on spurs producing varying num- 
bers of flowers 64 

Relation between length of spur growth made during preceding season, and fruit- 
fulness of the spur 65 

Relation between weight of the flower-bearing spur and its fruitfulness 67 

Weights of setting and of non-setting spurs 67 

Set of fruit on spurs of different weights 68 

Weights of spurs holding fruits for varying lengths of time . -. 68 

Relation between weight, or vigor, of the fruit-bearing spur, and number of 

fruits borne by it 69 

Relation between weight of the spur and number of flowers to the spur 70 

Relation between weight of the spur and length of the previous season's growth .... 71 
Relation between weight of the new spur growth and diameter of the conducting 

tissue 72 

Relation between diameter of conducting tissue and weight of spurs, from limbs 

having a light bloom and from those having a full bloom 73 

Relation between water supply, leaf area, and pushing of buds 74 

Relation between amount of lateral growth from the flower-bearing spur, and 

fruitfulness of the spur 76 

Relation between sap supply and fruit setting 78 

Fruit setting as influenced by varying amounts of leaf surface on the flower-bearing 

spur 81 

Influence of sunlight on the setting of fruit : 83 

Relation between seed formation and fruit development 84 

Number of seeds in fruit that sets and in fruit that drops 85 

Relation between number of seeds and size of fruits 86 

Size of fruit constant, number of seeds varying 87 

Weight of spur constant, number of seeds varying 87 

Weight of spur constant, number of seeds constant, size of embryo 

varying 89 

Number of seeds and seed value 91 

Relation between seed value, weight of spur, and set of fruit 92 

Observations concerning some of the physiological effects of seeds 95 

Withdrawal of water by leaves from fruits with varying numbers of seeds .... 95 
Depression of freezing point by sap from fruits with varying numbers of 

seeds 96 

Relation between formation of seeds and symmetrical development of fruit ... 98 

43 



44 Bulletin 393 

PAGE 

Relations to be considered in choosing fruits borne under similar conditions 99 

Position of the fruit on the spur, and number of seeds to the fruit 100 

Seed content and weights of long-stemmed and of short-stemmed fruits pro- 
duced on the same spur ioi 

Relation between number of seeds and size of fruits on spurs bearing one and 

on those bearing tw< > fruits 102 

Relation between aphid work and fruit development 103 

Number of seeds in normal apples and in apples stung by aphids 103 

Water-core as affected by aphid work and water supply 103 

Experiments concerning the absciss-layer 104 

Effect of removing fruit and leaving varying lengths of stem 105 

Effect of coating fruit with vaseline 105 

Effect of slow and of rapid drying of leaves on detached spurs with 

uncoated fruit and on detached spurs with vaseline-coated fruit 106 

Effect of a saturated and of a dry atmosphere on abscission of fruit on de- 
tached spurs 1 06 

Summary 106 

General discussion 109 

Bibliography 112 



FACTORS INFLUENCING THE ABSCISSION OF FLOWERS AND 

PARTIALLY DEVELOPED FRUITS OF THE 

APPLE (PYRUS MALUS L.) 1 

Arthur J. Heinicke 

Observations have shown that normally less than ten per cent of the 
apple blossoms which open in spring produce fruit. Many of the flowers 
are lost a few days after the petals fall, and a large number of the par- 
tially developed fruits are thrown off during the next few weeks. A 
rather conspicuous drop, commonly called the June drop, occurs in June 
and July, when the fruits are from one to three centimeters in diameter. 

This June drop may or may not be beneficial to the fruit grower. If 
more than five to ten per cent of the flowers on a tree producing a heavy 
bloom set fruit, a large quantity of apples must be removed by hand so 
that the remaining specimens can attain a desirable size and color. On 
the other hand, apple trees frequently produce an abundance of flowers 
but little or no fruit is harvested from them, practically all the apples 
being lost during the June drop or before. 

Diseases, insects, and unfavorable weather are often held acco ntable 
for the heavy loss of flowers and partially developed fruits. In unsprayed 
orchards the flowers and fruits that have fallen from the trees often 
show injury by scab and codling moth. Heavy losses sometimes result 
from the effects of winter injury, frost, wind, and hail. But in many 
cases the drop occurs even in the absence of such destructive agents. 

The failure of a large proportion of apple blossoms to set, and the 
heavy loss of partially developed fruits during the June drop, are fre- 
quently associated with poor pollination and lack of fertilization. The 
fact that a large proportion of the apples that fall generally have fewer 
seeds to the fruit than those that remain on the tree, indicates that the 
development of seeds is an important factor in fruit setting. Never- 
theless, many flowers set fruit even tho they are poorly pollinated, and 
many fruits remain on the tree even tho they have relatively few seeds. 

Obviously, then, there are other factors, aside from the destructive 
agents previously mentioned, and in addition to poor pollination and lack 
of fertilization, which influence the abscission of flowers and partially 
developed fruits of the apple. To study such factors was the object of a 



1 Also presented to the Faculty of the Graduate School of Cornell University, September, 1916, as a 
major thesis in partial fulfillment of the requirements for the degree of doctor 01 philosophy. 

Author's Acknowledgment. The writer wishes to acknowledge his indebtedness to Professor W. H. 
Chandler, who proposed the problem and who gave many helpful suggestions during the course of the 
investigations. 

45 



4 6 Bulletin 393 

series of observations and experiments that have been in progress during 
the past three seasons. The results obtained during this time are pre- 
sented in this bulletin. 

SURVEY OF LITERATURE 

In early times the success or failure of the fruit crop was attributed 
largely to weather conditions. This may be inferred from folklore similar 
to that recorded by Bull (1878). 2 The conditions mentioned in the fol- 
lowing quotation, for example, involve an early spring and rather dry 

weather: . 

March dust on an apple leaf, 
Brings all kinds of fruit to grief. 

In another quotation, emphasis is placed on the time of blooming, 
which likewise involves weather conditions: 

If the apple tree blossoms in March, 
For barrels of cider you need not sarch, 
But if the apple tree blossoms in May, 
You can eat apple dumplings every day. 

The chances of having cold, windy, cloudy, and rainy weather during 
blooming time would be greater in March than in May. Besides, the 
weather conditions immediately after fertilization of the flowers would 
probably be more favorable for fruit development during a late spring 
than during an early one. 

The following extracts from Langley (1729 a) are interesting since he 

attempts to explain the observed phenomenon on a physiological basis. 

Referring to the fact that "there are many excellent Kinds of Fruits 

which produce great Plenty of Blossoms, and but very little Fruit," 

Langley writes: 

This Sterility is caused by the too great Abundance of Wood, which, when 'tis 
cover'd over with its beautiful Blossoms, requires a much greater Quantity of Nourish- 
ment than the Roots are at that Time able to communicate, and thereby, for want 
of proper Nourishment, the Embryo Fruits are starved, and more especially when 
the .Soil and Spring are both dry, their Perspirations [transpirations] being then greatesl ; 
and if Easterly Winds happen to blow at that Time, their very drying exhaling Nature, 
is a further Help to the Destruction of the Fruit. 

This author also observed that some peaches in which the blossoms 
open before the leaves, such as Old Newington, have a tendency to pro- 
duce smaller crops of fruit than such varieties as Albemarle and Catherine, 
which produce leaves with their blossoms. He believed that the leaves 
"strongly attract Nourishment from the Roots to the Blossoms." 

Referring to the June drop, Langley (1729b) writes: 

Now [from May 20 to June 20] 'tis always seen that great 

Quantity of Fruit drops, altho' largely grown. Of this all our late Authors on 



2 Dates in parenthesis refer to bibliography, pages 112 to 114. 



Abscission of Flowers and Fruits of the Apple 47 

Gardening take Notice, and therefore advise, that the thinning of Fruits be omitted, 

until it appears that this great Fall is over 

'Tis very easy to conceive, that if very dry Weather exhales 

away that Moisture which is necessary for those Formations [the internal parts of the 
fruit, such as the kernels, stones, and the like], the Work will be imperfect, and con- 
sequently the Fruits must perish. 

Several experiments to prevent the drop were attempted during Lang- 
ley's time. The most successful method found was "to preserve them 
[the trees] from the very hot Sun, from ten in the Morning until two or 
three in the Afternoon" by means of a sail cloth. Langley, having tried 
this method, recommends it to " the Practice of the Diligent and Curious." 
He adds-, " 'Tis very serviceable to give the Trees a gentle Refreshing 
of Water, at the Time you begin to screen them from the Sun, which they 
will freely imbibe, and [which] very much strengthens Nature in her 
Productions." 

At the present time the weather is still in many cases held account- 
able for the failure of blossoms to set fruit. Osterwalder (1907 a), for 
example, cites the causes which the peasants of Switzerland hold account- 
able for the wholesale dropping of fruit. Among others, he mentions the 
"dew rain" of the early morning, which occurs during blooming time 
and subsequently; the strong mountain winds which prevail shortly after 
blooming time; and the presence of "honey dew" on the leaves. This 
honeydew, now known to be the result of aphid work, was formerly asso- 
ciated with local climatic conditions. 

Hedrick (1908) has given renewed emphasis to the importance of 
weather in fruit setting. He is of the opinion that unfavorable weather 
during blossoming time is the predominating factor in the loss of fruit 
crops. Besides mentioning the direct and obvious damage done by frost, 
hail, wind, and the like, to buds, flowers, and fruits, this author points 
out that rain, cloudiness, wind, and low temperatures during blossoming 
time offer unfavorable conditions for pollination and subsequent 
fertilization. 

Waite (1894) observed that many varieties of apples and pears are 
self -sterile. Fruits resulting from cross-pollination were found to be larger 
and finer specimens than those resulting from self-pollination. The 
former contained large, plump seeds, and the latter, small and flattened 
seeds. It was also noted that the ability of a tree to set fruit, either with 
its own pollen or with that from another tree, was affected by its state 
of nutrition and its general environment. 

Since Waite's work, the need of cross-pollination to insure a set of 
fruit has received considerable attention. While most of the writers or 
workers on this question — among whom may be mentioned Hansen 
(1894), Beach (1895), Budd (1896), Waugh (1896, 1901), Munson (1899), 



48 Bulletin 393 

Fletcher (1900), GofI (1901), Green (1902), Close (1903), Lewis and 
Vincent (1909), Bellair (19 10), and Gardner (1913) — recognize, as does 
Waite, that there are other factors, aside from self-sterility, which cause 
the falling of blossoms and immature fruits, all of them seem inclined to 
attach special importance to the necessity of cross-pollination for many 
varieties of fruits. It is pointed out that the structure of the flowers in 
manv cases is such as to inhibit self-pollination, whereas many flowers 
have special modifications that seem to favor cross-pollination. The in- 
fluence of such factors as weather, and the like, which favor or prevent 
cross-pollination, are emphasized. 

Other workers, the chief among these being Muller-Thurgau (1898, 
1008) and Ewert ( [906, 1907, 1910), while not ignoring the question of 
pollination, have directed special attention to the importance of nutrition 
as a factor in fruit setting. 

Muller-Thurgau has done most of his work with the grape. He finds 
(1898) that certain varieties can develop fruits without having the flowers 
fertilized. If, however, the blossoms of such varieties are emasculated 
and cross-pollination is prevented by inclosing the flowers in sacks, fruits 
do not develop. This author holds that the entrance of the pollen tube 
into the pistil may exert sufficient stimulus to initiate fruit development, 
even tho fertilization does not occur. The stimulus is believed to be one 
of a chemical nature which exerts an influence similar to that exerted 
by fertilization, tho less far-reaching. This influence is not confined to 
the single berry that has been pollinated or fertilized, but other berries 
on the same bunch are affected in such a way that they may develop 
even without the entrance of a pollen tube. 

Girdling the cane eight days before the flowers opened prevented the 
shedding of berries, while similar canes not treated lost their immature 
fruit. The berries produced were seedless, hence fertilization had not 
occurred. Muller-Thurgau believes that the ringing afforded better con- 
ditions of nourishment for the flowers, so that the pollen tube could 
germinate and enter the stigma and style. In a subsequent paper (1908) 
this author records cases in which he obtained a set of seedless grapes 
even without the stimulus of pollination. 

Muller-Thurgau noticed also that the berries on that part of the vine 
above the girdle were heavier than those borne below the girdle. The 
latter usually contained some seeds while the former were often seedless. 
Berries on vigorous shoots were larger than those on relatively weak 
growth even tho the weak canes were girdled. On a given cane, the berries 
with seeds were larger than those without seeds, and, furthermore, the 
size of the fruit was found to be proportional to the number of seeds con- 
tained in it. 



Abscission of Flowers and Fruits of the Apple 49 

Vines growing in the open but protected from cold rains lost their fruit, 
as did plants exposed to the rain. Muller-Thurgau states that rain during 
warm weather at blooming time does not necessarily have a detrimental 
effect on subsequent fruiting. He is of the opinion that the falling of 
blossoms and immature berries of the grape is due to an inadequate sup- 
ply of easily respirable food. Pollination may overcome a temporary 
shortage by affording a stimulating influence; fertilization is even more 
effective in causing the set on weak vines or during unfavorable condi- 
tions for assimilation and translocation of food. The conditions that 
obtain for the grape are said to hold for the apple and the pear as well. 

Ewert (1906, 1907, 1909) has given considerable attention to the 
development of seedless fruits. He believes that the development of 
such parthenocarpic fruits is possible if an abundance of food is avail- 
able __ suc h a supply, for example, as would accumulate if the downward 
movement of sap were inhibited. Ewert assumes that fruit formation 
on a tree occurs under competition for organic food. Such food, he thinks, 
has a greater tendency to flow to those fruits that contain seeds, which 
in turn are the result of cross-pollination. Consequently, seedless fruits 
developing on the same tree with fruits containing seeds are handicapped, 
and if the food supply proves inadequate such fruits will eventually 

fall off. 

Inclosing the flower spurs in sacks is said by Ewert to bring about 
unfavorable conditions for nutrition. Fruits developed on such inclosed 
spurs, which must be self-pollinated if pollinated at all and which conse- 
quently produce very poor seeds, are therefore handicapped in their 
development. If the ability of a tree to set fruit without pollination 
is to be determined, it therefore becomes necessary to prevent pollination 
on all flowers and not merely on a few. When this precaution was 
observed Ewert obtained seedless fruits which were as large as normal 
specimens. He found, however, that the same variety was less likely 
to set parthenocarpieally when some of the flowers on the tree were exposed 
to cross-pollination. 

Ewert found also that the dicogamy of the flowers is not always asso- 
ciated with self-sterility, nor is the absence of this condition, which would 
favor self-pollination, strictly associated with self-fertility. He believes 
that the question of the need for cross-pollination in fruit setting has been 
overemphasized. He is of the opinion that cold, rainy weather at bloom- 
ing time is unfavorable to the setting of fruit not so much because it 
hinders fertilization as because such conditions are generally harmful to 
the development of the young fruit. 

Osterwalder (1907 a, 1909) has also given the question of premature 
drop considerable attention. His studies of the seeds of fruits that remain 



50 Bulletin 393 

on the tree, and of those that are shed several weeks after blooming time, 
have shown that fertilized as well as unfertilized fruits drop. Osterwalder 
studied also the transpiration by the petals of the flowers. The amount 
of water lost in this way was found to be much less than that given off 
by a similar area of leaf surface. He believes that wilting of the floral 
parts is more likely to result from the loss of water thru the leaves than 
thru the petals. He holds that fruitfulness depends on nutrient con- 
ditions, on the number of fertilized fruits, and on the tendency of the 
variety to develop fruits parthenocarpically. 

Insects and diseases, chiefly codling moth and scab, are often mentioned 
in literature as causing heavy drops of blossoms and immature fruit 
(Bailey 1895, Reddick 191 2, Wallace 19 13). Too rapid vegetative growth, 
especially of young trees, is sometimes cited as unfavorable to fruit setting 
(Waite, 1894). A number of other general causes, such as poor soil, 
plowing during blooming time (Gould, 1915), drought, and the like, 
are occasionally held accountable for crop failure after blossoms have been 
produced. 

MATERIAL USED IN THESE EXPERIMENTS 

The observations and experiments recorded in these pages were made 
during the course of- three summers, 1914^0 1916 inclusive. For the most 
part the work was done at the experiment station orchard at Ithaca, 
New York, but observations on a few outlying orchards in western New 
York were also made. Unless otherwise mentioned, the trees under 
observation were between forty and fifty years old. About seven years 
ago these trees were pruned severely, and since that time they have received 
ordinary care — that is, cultivation, pruning, and thoro spraying. 

In this paper the natural drop only is considered, not the drop caused 
by such external agents as frost, insects, and diseases. In a well-sprayed 
orchard the drop resulting from scab and from codling moth is practically 
negligible. Examination of several hundred flowers and small fruits 
collected from sheets suspended under the trees in the station orchard 
at Ithaca in the spring of 19 16, showed that only about one per cent 
were affected by scab. In western New York, however, the unfavorable 
weather did not permit the growers to spray effectively that spring, 
and, as a result, scab infection on the stems of flowers and young fruits 
caused a heavy drop. Cases of a similar nature have been reported 
previously (Bailey 1895, Reddick 191 2, Wallace 19 13). 

MAGNITUDE OF THE FIRST AND OF THE JUNE DROP 

Before any experimental work was undertaken, a detailed survey 
was made of the extent and distribution of the first drop and of the June 



Abscission of Flowers and Fruits of the Apple 



5i 



drop. By first drop is meant the loss of flowers and of very slightly 
developed fruits that occurs within from one to three or four weeks after 
the petals fall. In the majority of these drops, the ovary and sur- 
rounding tissue has not developed beyond the flower stage. In a relatively 
few cases, the young fruits have attained a diameter of from one-half to 
one centimeter before they fall. 

Flowers developing into fruits after the first drop 

The extent of the first drop is indicated by the data given in table 1. 
The figures are based on a consideration of all flower-bearing spurs found 




Fig. 1. vigorous spur, producing fruit and lateral growth 

Lateral shoots are shown at A and B. The spur growth made since spring is shown at C. The leaves 
on this growth are the bud leaves. The large scar at E is from the stem of an apple that fell at the June 
drop; the small scars at D are flower-stem scars. A part of the preceding year's growth is shown at F. 
(3 natural size) 



52 



Bulletin 393 



on a number of different branches from one or more trees of each variety. 
Normal branches from five to ten years old were chosen. They varied in 
length between one meter and one and a half meters. The total number of 
flowers was determined by counting the number of flower-stem scars on the 
ends of the spurs and the number of fruits remaining on the spurs (fig. 1). 



TABLE 1. 



Percentage of Flowers Developing into Fruits after 
the First Drop 



Variety 


Total 

number of 

flowers 


Number 
set 


Per- 
centage 

set 


Per- 
centage 
lost 


Maiden Blush 

Westfield 


271 
478 
268 
656 

1,563 
840 


166 
270 

47 
no 

335 
183 


61 .2 
56.5 
17 -5 
16.8 
21.4 
21.8 


38.8 
"43-5 
82.5 
83.2 
78.6 
78.2 


Falla water 

Baldwin 


Tompkins King 

Rhode Island . . 







From two-fifths to four-fifths of the flowers are lost during the early 
drop. The varieties given in the table fall into two groups, depending 
on the number of flowers lost. One group, represented by Maiden Blush 
and Westfield, lost only half as many as did the other group. All varie- 
ties were growing in the same orchard and they bloomed during the same 
time; consequently they had equal chances of being cross-pollinated. Can 
the variations noted be due to a tendency toward self-fertility in the first 
group!" Subsequent data may throw some light on this question. 

Spurs setting fruit after the first drop 

From a practical standpoint, it is interesting to note the percentage of 
flower-bearing spurs that set fruit. Such data are presented in table 2 : 



TABLE 2. Percentage of Flower-bearing Spurs Retaining Fruit 

AFTER THE FlRST DROP 



Variety 



Maiden Blush . 

Westfield 

Fallawater .... 

Baldwin 

Tompkins King 
Rhode Island 



Number 

of spurs 
with 

flowers 



157 

89 

Il6 

V>2 

47* 
534 



Number 

with 
fruit 



L54 
84 

79 
183 
307 
296 



Per- 
centage 
with 
fruit 



Per- 
centage 
without 

fruit 



Abscission of Flowers and Fruits of the Apple 



53 



The figures are based on counts of all flower-bearing spurs found on a 
number of different branches taken from one or more trees of each variety. 
The branches used were similar to those already described. 

It is seen from the table that in some varieties practically all spurs 
set fruit, while in others almost half of the flower-bearing spurs fail to 
set fruit. 

Variations in percentage of spurs setting fruit after the first drop. — The 
variations found in different branches, in the percentage of spurs that 
set fruit after the first drop, are shown in table 3. Most of the branches 
were about one and one-half to two centimeters in diameter at the base, 
and the wood was from one to at least five years old. Only healthy and 
apparently normal branches were considered. 

TABLE 3. Variations in the Percentage of Flower-bearing Spurs That 
Set Fruit after the First Drop 







Total 


Number 


Per- 


Variety and tree 


Branch 


number of 


setting 


centage 






spurs 


fruit 


setting 

fruit 


Fallawater, B 2 


1 


26 


19 
22 


73- 1 
61 .1 




2 


36 




3 


27 


18 


66.7 




4 


27 


20 


74- 1 


Baldwin, B 8 


1 


24 

16 
16 


21 


87.5 

62.5 
56.2 


Baldwin, E 7 


1 
2 


10 
9 






3 


20 


12 


60.0 




4 


13 


9 


69 j 




5 


19 


8 


42.1 




6 


12 


6 


50 




7 


17 


12 


70.6 


Baldwin, E 10 ,,....,. 


1 
2 


6 
9 


4 
6 


66.7 




66.7 




3 


14 


9 


64 3 




4 


24 


17 


70.8 




5 


23 


15 


65.2 




6 


20 


13 


65.0 




7 


16 


11 


68.8 




8 


25 


13 


52.0 




9 


18 


14 


778 




10 


18 


9 


50.0 




11 


16 


6 


37-5 


Westfield 


1 

2 


60 
29 


57 

27 


95-0 
93-1 




Maiden Blush, A 8 


1 


69 


69 


100. 




2 


29 


29 


100. 




3 


12 


12 


100. 




4 


28 


28 


100. 




5 


19 


16 


84.2 



54 



Bulletin 393 
TABLE 3 (concluded) 







Total 


Number 


Per- 


Variety and tree 


Branch 


number of 


setting 


centage 






spurs 


fruit 


setting 
fruit 


Tompkins King, C 2 


1 


33 


24 


727 




2 


<9 


18 


94 


7 




3 


29 


21 


72 


4 




4 


10 


9* 


90 







5 


14 


10 


7i 


4 




6 


15 


10 


66 


7 




7 


36 


26 


72 


2 




8 


76 


52 


68 


4 




9 


20 


11 


55 







10 


23 


10 


43 


5 




11 


20 


9 


45 







12 


34 


14 


4i 


2 




13 


25 


1 1 


44 





Tompkins King, C 3 


1 


35 


3i 


88 


6 




2 


28 


16 


57 


1 




3 


18 


9 


50 







4 


33 


16 


48 


5 




5 


10 


10 


100 





Rhode Island, B 5 


1 


21 


9 


42 


8 




2 


47 


22 


46 


8 




3 


100 


38 


38 







4 


51 


32 


62 


7 




5 


55 


3i 


56 


4 


Rhode Island, B 3 


1 


47 


39 


83 







2 


49 


35 


7i 


4 




3 


80 


42 


52 


5 




4 


60 


28 


46 


7 




5 


-M 


20 


83 


3 



The figures for the individual branches of a given tree vary consider- 
ably. Casual observations have shown that these differences cannot be 
explained by the location, angle, or exposure of the branch on the tree, 
since the differences are sometimes found in similarly located branches. 
For example, in Rhode Island B 5, branches 1,2, and 3 all came from the 
top of the tree; in Tompkins King C 2, branches 1 and 5 were from the 
south side of the tree, branches 2, 3, and 4 were from the north side, 
branches 6, 7, and 8 arose from the same parent limb on the southwest 
side of the tree, branches 9 and 10 were growing upward at an angle of 
45 , and branches 1 1, 12, and 13 were drooping. Figures presented later 
(page 58) afford a probable explanation for the differences noted. 

Flowers developing into fruits after the June drop 

Totals of flowers on many limbs. — Branches were examined in the latter 
part of July and in early August for the number of fruits set after the June 



Abscission of Flowers and Fruits of the Apple 



55 



drop. Data based on all flower-bearing spurs found on various branches 
are given in table 4. The number of flowers originally borne on each spur 



TABLE 4. 



Percentage of Flowers Developing into Fruits after 
the June Drop 



Variety 


Total 

number of 

flowers 


Number 
set 


Per- 
centage 
set 


Per- 
centage 
lost 


Tompkins King 

Baldwin 


2,849 
770 


84 
53 


2.9 
6.9 


97 1 
93 1 





was obtained by counting the flower scars and the fruits on the spur. 
Approximately three to seven per cent of the total number of flowers 
finally developed into fruits. 

Flowers falling at the first drop and at the June drop on fruit-bearing 
spurs. — The figures in table 5 show the relation between the first drop 
and the June drop. The data are based on a consideration of all fruit- 
setting spurs found on several branches from trees of each variety. They 
do not take into consideration the spurs that bore flowers but failed to 
set fruit. The first column of figures contains the total number of spurs, 
and the second contains the total number of flowers found on these spurs. 
Unless otherwise mentioned, the percentages are based on the original 
number of flowers. 

TABLE 5. First Drop and June Drop on Fruit-setting Spurs 





Num- 
ber of 
spurs 


Num- 
ber of 
flowers 


Fruits falling at 
first drop 


Fruits falling at 
June drop 


Fruits finally 
setting 


Variety 


Num- 
ber in 
drop 


Per- 
centage 
of 
drop 


Num- 
ber in 
drop 


Percentage 
of drop 


Number 
set 


Percent- 
age set 




(A) 


(B) 


Westfield 

Maiden Blush. . . . 
Tompkins King . . 

Fallawater 

Rhode Island .... 
Baldwin 


47 
54 

5$ 
30 
46 


281 
281 
557 
252 
154 
258 


7 
90 
416 
192 
116 
203 


2.5 
32.0 

74-7 
76. 2 
753 

78.7 


227 

126 

38 

10 

8 

9 


80.8 

44-8 
6.8 
4.0 
5-2 
3-5 


82.8 
66.0 
26.9 
16.7 
21 . 1 
16.4 


47 
65 
103 
50 
30 
46 


16.7 
23.1 
18.5 
19.8 
19.5 
17.8 



(A) Percentage based on original number of flowers. 

(B) Percentage based on number of fruits remaining after first drop, obtained by subtracting figures 
in fourth column from those in third column. 

The figures indicate that the June drop is relatively small when the 
first drop is large. On the other hand, if a large proportion of the flowers 
begin to form fruits, the June- drop will be heavy. Approximately twenty 
per cent of the flowers on fruit-setting spurs finally develop, which means 
one fruit to the spur. The variety Maiden Blush has a tendency to develop 
more than one fruit to the spur. The percentage is somewhat lower than 



56 



Bulletin 393 



twenty in Westfield, because this variety averages higher than five flowers 
to the spur. The percentage of flowers which finally set, as given in 
table 5, is obviously too high if all flower-bearing spurs are considered. 



Spurs setting fruit alter the June drop 

Consideration of spurs from many limbs. — The percentage of flower- 
bearing spurs that retain fruits after the June drop is given in table 6. 
These data were obtained during the latter part of July and the early 
part of August. The figures are based on a consideration of all spurs 
found on many branches of each variety. 



TABLE 6. 



Percentage of Flower-bearing Spurs Retaining Fruit 
after the june drop 



Variety 


Number 
of spurs 

with 
flowers 


Number 

with 
fruit 


Per- 
centage 

with 
fruit 


Per- 
centage 
without 

fruit 


Baldwin 

Tompkins King 

Rhode Island 


1.945 
368 
428 


630 

68 
73 


324 

18.5 
17. 1 


67.6 
81.5 
82.9 







Only about one-sixth to one-third of the flower-bearing spurs become 
fruit-setting spurs, as indicated by these data. 

Variations in percentage of spurs setting fruit after the June drop. — The 
percentages of fruit-bearing spurs on individual twigs of a number of 
varieties are given in table 7. Notes concerning the source of the indi- 
vidual twigs were obtained in some cases. These indicate that the angles 



TABLE 7. 



Variations in the Percentage of Flower-bearing Spurs That 
Sei Fruit after the June Drop (1915) 







Total 


Number 


Per- 


Variety and tree 


Branch 


number of 


setting 


centage 






spurs 


• fruit 


setting 

fruit 


Baldwin, B 8 


1 


15 

28 


7 
9 


46.7 
32.1 




2 




3 


1 1 


6 


54 ■ 5 




4 


10 


6 


60.0 




5 


30 


5 


16.7 




6 


188 


4i 


21.8 


Baldwin, E 7 . . . ' 


1 


18 


10 


55 ■ 5 




2 


19 


1 1 


57-9 




3 


8 


6 


75-0 




4 


23 


12 


52.2 




5 


10 


7 


70.0 



Abscission of Flowers and Fruits of the Apple 



57 



TABLE J (concluded) 







Total 


Number 


Per- 


Variety and tree 


Branch 


number of 


setting 


centage 






spurs 


fruit 


setting 
fruit 


Ealdwin, E 7 {continued) 


6 


215 


82 


38.1 




7 


345 


55 


15 9 




8 


145 


30 


20.7 




9 


281 


69 


24-5 




10 


> 385 


175 


45-4 


Baldwin, Eio 


1 


25 
6 


14 
4 


56.0 




2 


66.7 




3 


9 


6 


66.7 




4 


14 


6 


42 9 




5 


24 


13 


54 2 




6 


23 


7 


304 




7 


20 


9 


45 




8 


16 


9 


56 3 




9 


25 


8 


32 




10 


18 


10 


55-5 




11 


18 


9 


50.0 




12 


16 


j 


250 


Tompkins Kirg, C I 


1 


146 

42 
31 


21 


14 4 


Tompkins King, C 2 


1 


7 


16.7 




2 


2 


6-5 




3 


25 


3 


12 .0 


Tompkins King, C 3 


1 


35 


10 


28.6 




2 


28 


9 


32.1 




3 


18 


4 


22 .2 




4 


33 


9 


27 -3 




5 


10 


3 


30.0 


Rhode Island, B 5 


1 


27 


1 


37 




2 


23 


1 


4 3 




3 


18 


2 


111 




4 


17 


1 


5 9 




5 


35 


1 


2.9 


Rhode Island, B 3 


1 


88 


30 


34 1 




2 


127 


21 


16.5 




3 


6 


1 


16.7 




4 


34 


5 


14 7 




5 


53 


10 


18.9 



at which the branches grow and their location on different parts of the 
tree cannot be held accountable, in themselves, for the variations found. 
For example, in Baldwin B 8, branches 1 and 3 were growing in an upright 
position, and branches 2 and 4, found on the same side of the tree, were 
drooping; in Baldwin E 7, branches 1 to 4 were obtained from the top 
of the tree, and branches 5 to 10 from limbs close to the ground. 



58 



Bulletin 393 



RELATION BETWEEN AMOUNT OF BLOOM AND SET OF FRUIT 

In the spring of 19 16 most of the mature trees in the station orchard 
at Ithaca produced a heavy bloom. Individual limbs on many of the trees, 
however, bore relatively few flowers. A number of such limbs, with a 
light bloom, were labeled. Corresponding limbs with a heavy bloom, 
but otherwise like the former — having a similar exposure, and arising 
from the same parent limb — were also labeled. After the June drop, 
the total number of flower-bearing spurs on each limb was obtained, 
together with the number of spurs that had set fruit. The data from some 
of the branches are recorded in table 8: 



TABLE 8. 



Percentage of Spurs Setting Fruit on Limbs with Heavy Bloom 
and on Those with Light Bloom 





Limbs with light 


bloom 


Limbs with heavy bloom 


Variety 


Num- 
ber of 
spurs 


Num- 
ber 
set 


Per- 
centage 

set 


Num- 
ber of 

spurs 


Num- 
ber 

set 


Per- 
centage 
set 


Baldwin, tree 1 


52 
47 
21 

25 


40 
38 
10 

19 


76.9 

80.8 
47.6 
76.0 


116 
76 

255 
250 


18 

39 
21 
20 


15-5 

51-3 

8.2 


Baldwin, tree 2 . . . 


Falla water 


Westfield 


8.0 






Total 


145 


107 


73-8 


697 


98 


14. 1 





A larger percentage of spurs set fruit in the limbs with the relatively 
light bloom. This fact is easily apparent on inspection, even without 
accurate counts. Hence, only a relatively few limbs were removed from 
the trees to obtain records, the remainder being used for other purposes. 
An explanation for the results obtained is afforded by subsequent 
observations. 



SET OF FRUIT ON LIMBS WITH LARGE LEAVES AND ON LIMBS WITH 

SMALL LEAVES 

It is not uncommon to find individual limbs with leaves noticeably 
smaller than those on the remaining limbs of the same tree. In the spring 
of 191 6, such small-leaved limbs which had produced a heavy bloom were 
labeled. Limbs with normal leaves, but otherwise similar, were likewise 
labeled. The percentage of flower-bearing spurs that set fruit was deter- 
mined for each group of branches. Data of several of the many limbs 
labeled are contained in table 9 : 



Abscission of Flowers and Fruits of the Apple 



59 



TABLE 9. Percentage of Spurs Setting Fruit on Weak and on Vigorous 

Limbs 





Vigorous 
limbs with large 


leaves 


Weak 
limbs with small leaves 


Variety 


Num- 
ber of 
spurs 


Num- 
ber 
set 


Per- 
centage 
set 


Num- 
ber of 

spurs 


Num- 
ber 
set 


Per- 
centage 
set 


Unknown 


164 
223 


94 
67 


57-3 
30.0 


219 
207 


33 
34 


15 1 
16.4 


Tompkins King 


Total 


387 


161 


41 .6 


426 


67 


15 7 



The percentage of flower-bearing spurs that set fruit was greater on 
the branches with large leaves than on those with small leaves. The same 
condition prevailed on the other limbs that had been labeled, as was 
determined by careful inspection. These results can probably be explained 
on the basis of data presented later in these pages. 

set of fruit as influenced by the location of the spur on the 
twig growth of different years 

Observations were made to determine whether flower-bearing spurs 
arising from wood of different ages would be more likely to set fruit 
in some cases than in others. Data regarding this point are given in 
tables 10, n, 12, and 13. These figures were obtained during the summer 



TABLE 10. Percentage of Flowers Developing into Fruits after the First 
Drop, on Spurs Arising from Wood of Different Ages 



Year's wood 



Tompkins King, tree 1 



Num- 
ber of 
flowers 



Num- 
ber 
set 



Per- 
centage 

set 



Tompkins King, tree 2 



Num- 
ber of 
flowers 



Num- 
ber 
set 



Per- 
centage 
set 



1914 

1913 
1912 



65 
379 
129 



11 

97 
44 



16.9 
25.6 
34 1 



25 
101 

85 



3 
34 
12 



12.0 

33-7 
14. 1 



of 191 5, hence the spurs on 19 14 twig growth came from lateral buds. 
Ordinarily, few lateral buds form blossoms in New York State, and such 
formation may be ascribed to the unusually favorable conditions for 
fruit-bud formation which prevailed during 19 14 — a wet spring followed 



6o 



Bulletin 393 



by a dry, sunny season. Comparatively few of the flowers arising from 
such buds set fruit, as may be seen from the figures. Other observations 
indicate that the length of the 1014 wood influenced the setting ability 
of the (lowers arising from the lateral buds. In a number of cases in 
which the growth was twenty-five centimeters and the terminal bud pro- 
duced a flower, few, if any, lateral buds set. When the growth was less 
vigorous, it was not uncommon to find fruits produced on the lateral buds. 



TABLE 1 1. Set ox Spi rs Arising from Wood of Different Ages 





Tompkins King, tree 1 


Tompkins Kinj 




Baldwin 


Rhode Island 


Year's 
























wood 


Num- 


Num- 


Per- 


Num- 


Num- 


Per- 


Num- 


Num- 


Per- 


Num- 


Num- 


Per- 




ber of 


ber 


centage 




ber 


centage 


ber of 


ber 


centage 


ber of 


ber 


centage 




spurs 


set 




spurs 

IS 


set 


set 


spurs 


set 


set 


spurs 


set 


set 


1014. 


S 


3 


60.0 


. 


46.7 


12 


5 


4' 7 


16 


4 


25.0 


1013. 


36 


25 




70 


54 


68 . 4 86 


63 


73 3 


ro 


5 


50.0 


1012 


H> 


7 




25 


20 


80.0 ,u 


-'4 


70 6 








IOII 


1 1 


4 


36 1 






52 


M 


438 








1910. . 


;i 


r6 








"4 


5 


35 7 









TABLE 12. Percentage of Flowers Developing into Fruits after the June 
Drop, on Spurs Arising from Wood of Different Ages 





Tompkins King, tree I 


Tompkins King, tree 2 


Year's wood 


Num- 
ber of 
flowers 


X tim- 
ber 

1 'i 


Per- 
centage 
set 


Num- 
ber of 
flowers 


Num- 
] >er 
set 


Per- 
centage 
set 


191 4 
1913 

1912 

1 9 i 1 

1910 


65 
$79 


3 
46 
29 


4.6 

12 . 1 
22 5 


25 
191 

85 

65 

169 

96 


3 
34 
12 

4 

27 
12 


12.0 
178 
14. 1 
6.2 
16.0 


!<)<><) 


12.5 









Such observations can be interpreted on the basis of nutrition, that is, 
an adequate supply of stored food which is readily available in spring, 
as well as a sufficient supply of water. So long as active growth continues, 
the assimilate is probably translocated to the -rowing parts; little is left 
for storage and fruit-bud formation in the lateral buds. After growth 
finally ceases on long twigs, the time remaining for active assimilation 
is inadequate for abundant storage. On the other hand, short twigs 
stop elongating much sooner; consequently, the lateral buds on short 
twigs can store the food which is utilized for continued length growth 



Abscission of Flowers and Fruits of the Apple 



61 



Q 





OOO 






, 60 










N ro 












O, C w 





















g o E 

5 I- 3 



Z^ 



O 00 N rf 
O N t~ Ov 



C tM3 
C Ov m 



C I- ■ 



S u 3 
►t <U P. 



PQ 



O "*0 

O OiOO 



Zi: 






62 Bulletin 393 

on long twigs. No analyses are available to show that such a condition 
actually exists. 

In several cases, the spurs arising from 19 13 twig growth set more fruit 
than did spurs arising from older wood. In other cases, however, spurs 
on older twigs were more fruitful than those on younger growth. This 
fact suggests that the ability of a bud to develop into a fruit-setting 
spur is determined to some extent during the year when it is formed in 
the axil of a leaf. It should be mentioned, in this connection, that many 
limbs have no flower-bearing spurs on a given year's growth, whereas 
such spurs are borne on younger and on older wood of the same limb. 
Then, too, the proportion of buds that develop into fruiting spurs varies 
with the different year's growth on the same branch. 

Apparently the age of the spur alone, at least from the second to the 
fourth or the fifth year, has little influence on its fruitfulness. Spurs 
arising from wood several meters from the periphery of the tree would 
generally be in a less desirable position so far as exposure to light and free 
circulation of air are concerned. This condition would probably have an 
unfavorable influence on the nutrition of the fruit bud. 

SET OF FRUIT ON SPURS FORMED ON DIFFERENT PARTS OF A GIVEN YEAR'S 

GROWTH 

The vigor of the individual buds found on the twig growth of a given 
year varies considerably. This can be determined by observing the fate 
of the buds the year after they have been formed. In most of the varieties, 
buds near the beginning, and in many cases those just before the end, 
of a year's growth remain dormant (Koopmann, 1896). If a year's growth 
happens to be from thirty to forty centimeters, a third zone of weak 
buds may be found near the center of that particular year's growth. 
The transition from dormant buds to those that produce strong spurs, 
or even short twigs, is usually, but not always, a gradual one. The 
strongest spurs are generally found just before the terminal zone of 
dormant buds, and before the middle zone if there is one. The leaves in 
the zones bearing weak buds will usually be the first to turn yellow and 
fall off if the twigs are removed from the tree and placed in beakers 
containing water. Such leaves likewise are the first to be shed in the 
autumn. 

Just what causes these variations in bud vigor is not definitely known. 
They are found even in upright twigs growing at the top of the tree, 
where light conditions for the different buds are approximately the same. 
The nutrient supply available at the time of formation of the individual 
bud may determine its vigor. It is probable that the water supply from 



Abscission of Flowers and Fruits of the Apple 



63 



the soil, the temperature, the humidity, cloudiness, and other environ- 
mental conditions, have marked influence on the nutrition. 

In the summer of 1914, the fruit borne on spurs arising from 19 12 
or 19 13 wood was found near the end of the season's growth in most 
cases. The percentage of flower-bearing spurs that set fruit in the 
terminal parts of a given year's growth, as compared to the set on the spurs 
in the lower halves of the same twigs, is shown in table 14. It is seen 



TABLE 14. 



Set of Fruit on Spups Formed on Different Parts of 
a Given Year's Growth 





Spurs in upper half of year's 
growth 


Spurs in lower half of year's 
growth 


Variety- 


Number 

of 

spurs 


Per- 
centage 
set after 
first 
drop 


Per- 
centage 
set after 
June 
drop 


Number 
of 

spurs 


Per- 
centage 
set after 
first 
drop 


Per- 
centage 
set after 
June 
drop 


Baldwin 

Tompkins King . 


136 
47 


64 3 
63.8 


50.0 
34 -o 


90 

24 


53-2 
45-8 


40.0 
12.5 



that there are fewer flower -bearing spurs in the basal half of the year's 
growth, and a smaller percentage of these basal spurs set fruit. The 
results would probably have been more striking if only the relatively 
short twigs had been considered. The long twigs, as has been mentioned, 
usually show a middle zone of weak or dormant buds, which are generally 
preceded by fruit-setting spurs. In such twigs, fruit-setting spurs would 
be found in the basal half of the year's growth. 

relation between number of flowers to the spur, and ability of 
the spur to set fruit 

The number of flowers on an apple spur varies from two to seven. 
Casual observations seemed to indicate that there is a relation between 
the number of flowers produced by the spur and its ability to bear fruit. 
Consequently, a more careful study of this question was undertaken. 



Average number of flowers on spurs holding fruit for varying lengths of time 

Records were made of the number of flowers borne on spurs that lost 
all fruit at the first drop, on those that held fruit until the June drop 
but not longer, and on those that finally set fruit. The data are recorded 
in table 15: 



64 



Bulletin 393 



TABLE 15. Average Number of Flowers on Spurs Holding Fruit for Varying 

Lengths of Time 





Spurs losing all fruit at 
first drop 


Spurs holding fruit until 
the June drop 


Spurs finally setting 
fruit 


Van 


Num- 
spurs 


Num- 
ber of 
flowers 


Average 

number of 

flowers 
to the spur 


Num- 


Num- 
ber of 
flowers 


Average 
number of 

tli >uvr '■ 


Num- 
ber of 
spurs 


Num- 
ber of 
flowers 


Average 
number of 

flowers 
to the spur 


Tompkins Ivinti 
Tompkins King. . . 


39 
60 


'44 
257 

-'7 1 


3 00 
494 

4 5-' 


-'3 

3 7 

1 r. 
47 


114 
216 
S69 
221 


4 96 

S.84 
4.01 
4.70 


64 
35 

35 


354 
204 

21 1 


5 53 
583 


1 ! 


6.03 


All v . 


1. SI 


672 


4 45 


223 


1, 12b 


502 


13 1 


769 


5-74 



There seems to be a correlation between the number of flowers on 
a spur and the ability of the spur to hold fruit. Spurs that lose all flowers 
and fruits during the first drop have the smallest average number of 
flowers, and those that finally set have the largest average number of 
flowers. 

Set of fruit on spurs with varying numbers of flowers 

The spurs from several branches were grouped in lots based on the 
number of flowers borne. The percentage of spurs bearing fruit in each 
ca - is recorded in table 16: 

TABLE 16. Set of Fruit on Spurs with Varying Numbers of Flowers 





Branch 


. Spurs with 
4 flowers 


Spurs with 
5 flowers 


Spurs with 
6 flowers 


\ ariety 


Num- 
ber of 

spurs 


set 


Num- 
ber of 

spur:. 


Per- 
centage 

' set 


Num- 
ber of 

-purs 


Per- 
centage 
set 


Baldwin 

Tompkins King. . 
Rhode Island 


1 

2 

1 
2 


7 
7 

18 
18 
30 


429 

42 <) 
11.1 
11.1 
50. c 


32 

39 

33 

33 

103 


56. 2 
41 

51 5 
2 1 2 
70 () 


63 
70 
62 
62 
26 


*6s.i 
t48-i 
♦70.9 
t33 9 
*79-2 



■ After tin Brs1 drop 
t After the June dn >p 

These data likewise show that the fruit-bearing ability of a spur is 
closely related to the number of flowers produced by the spur. The spurs 
having the greatest numbers of flowers show the highest percentage set. 

Percentage of flowers developing into fruits on spurs producing varying 

numbers of flowers 
In many cases the spurs bear more than one fruit. Do individual 
flowers on spurs producing six blossoms have to compete more for their 



Abscission of Flowers and Fruits of the Apple 



65 



portion of food and water, than flowers on spurs producing a smaller 
number of blossoms? The data in table 17 contain an answer to this 

TABLE 17. Percentage of Flowers Developing into Fruits on Spurs with 
Varying Numbers of Flowers 





E ranch 


Spurs with 
4 flowers 


Spurs with 
5 flowers 


Spurs with 
6 flowers 


Variety 


Num- 
ber of 
flowers 


Per- 
centage 
set 


Num- 
ber of 
flowers 


Per- 
centage 
set 


Num- 
ber of 
flowers 


Per- 
centage 

set 


Westfield 




28 
28 
60 
24 
24 


28.9 
10.4 
56.7 
45-i 
20.9 


150 

195 

80 

no 

no 


54-0 
82.0 
60.0 
60.0 
20.0 


228 
420 
102 
138 

138 


t57 
*90 
*72-5 
*7i .0 

f23-2 


Baldwin 

Maiden Blush 


1 
2 
1 

1 



♦After the first drop. 
fAfter the June drop. 

question. The figures indicate that a higher percentage of flowers develop 
into fruits on spurs producing six flowers than on spurs producing four 
or five flowers. 

RELATION BETWEEN LENGTH OF SPUR GROWTH MADE DURING PRECEDING 
SEASON, AND FRUITFULNESS OF THE SPUR 

In 1 91 5 it was observed that many of the fruits were borne on spurs 
which had elongated more than two centimeters during the previous season. 
This fact was first noted in studying the set on Mr. F. W. Cornwall's 
Baldwin orchard at Pultneyville, New York. All flower-bearing spurs 
found on large branches from several trees were placed in two groups. 
The first group contained spurs that had made a growth of two centimeters 



TABLE 18. 



Set of Fruit in 1915 on Spurs Making Different Growth Lengths 
during the Preceding Year 





Spurs making 2 centimeters 
growth or more during 191 4 


Spurs making less than 2 centi- 
meters growth during 191 4 


Branch 


Number 
of spurs 


Number 
set 


Percent- 
age set 


Number 
of spurs 


Number 

set 


Percent- 
age set 


1 


17 
24 

37 
36 


13 
13 
21 

25 


76.5 
54-2 
56.8 
69.4 


34 
57 
58 
67 


9 

18 
16 
17 


26.5 


2 

3 

4 


31.6 

27.6 
25-4 


Total 


114 


72 


632 


216 


60 


27.8 



66 



Bulletin 393 



or more during 191 4 — the year preceding that in which fruit was borne; 
the second group contained spurs that had made less than two centimeters 
growth in the same period. The percentage of spurs setting fruit in 
each group is given in table 18. 

In 1916 similar data were obtained at the station orchard at Ithaca. 
All spurs that had elongated one centimeter or more in 191 5 were placed in 
one class, and those that had grown less than one centimeter were placed 
in another. The percentages of spurs that produced fruit are recorded 
in table 19. It is seen from the table that spurs which have elongated 
more than one centimeter during any one year are more likely to set fruit 
in the following year than are spurs that have made a weaker growth. 3 



TABLE 19. 



Set of Fruit in 1916 on Spurs Making Different Growth Lengths 
during the preceding year 





Branch 


Spurs making 1 centimeter 

growth or more during 

1915 


Spurs making less than 

1 centimeter growth 

during 191 5 


Variety 


Num- 
ber of 
spurs 


Num- 
bei set 


Per- 
centage 
set 


Num- 
ber of 
spurs 


Num- 
ber set 


Per- 
centage 
set 


Strawberry 


1 

2 
3 
4 


434 
405 
237 
567 


138 
122 

88 
182 


31.8 
30.1 

37-1 
32.1 


721 
659 
445 
878 


118 

113 

5i 

162 


16.4 
17. 1 

11. 5 

18.4 


Total 

Baldwin 


1 
2 
3 

4 
5 


1,643 

67 
75 
50 
44 
84 


530 

57 
36 
31 
22 

69 


323 

85.1 
48.0 
62.0 
50.0 
82.1 


2,703 

52 
59 
117 
68 
61 


444 

25 
14 
30 

14 

8 


16.4 

48.1 

23-7 
25.6 
20.6 
131 




Total 

Tompkins King .... 


1 
2 


320 

80 
23 


215 

40 
6 


67.2 

50.0 
26. 1 


357 

63 
48 


9i 

18 

8 


25-5 

28.6 
16.7 


Total 

Grand total . 




103 
2,066 


46 
791 


44-7 
38.3 


in 
3,171 


26 

56l 


23-4 
17-7 



Casual observations during 191 5 seemed to indicate that flowers pro- 
duced in the terminal bud of twigs making more than approximately 
twenty centimeters length growth in 1 9 1 4 did not set as well as did flowers 
on shorter twigs. In 1916, however, the same varieties were setting at 
the ends of long twigs. 

3 Yeager (1016), in a bulletin which was received here while this paper was being prepared for publica- 
tion, likewise reports a correlation between the amount of growth that a spur makes in one year and its 
production in the following year. 



Abscission of Flowers and Fruits of the Apple 67 

relation between weight of the flower-bearing spur and its 

fruitfulness 

Most writers on topics relating to fruit setting agree that the vigor of 
the tree is a factor to be considered. It is generally assumed that excessive 
vegetative growth is opposed to fruit production. No definite figures, 
however, are available regarding the influence of the vigor of the indi- 
vidual spur on fruit bearing. 

When the fruit bud opens in spring, a short spur is produced varying 
in length from 0.3 to 2 centimeters. This new growth bears leaves later- 
ally and a cluster of flowers terminally. It seems safe to assume that 
this spur growth is made at the expense of stored food. The stored food is 
the result of photosynthetic activity ,. 
during the previous year. The / \ 
amount of this early spur growth / \\ \ 
with its leaves and flowers can there- / M \ 
fore be taken as an index to vigor. ^^^ jl / ^ 

Weights of setting and of non-setting \ \\ \\\(J/ fy^ I 

The relation of vigor to the fruit- \ \^^^^M// J/^ — ^^ ^ j 

setting ability of the tree was studied \ ^Sv \ \\ y^ /l^-*^"^ / 

by ascertaining the weights of a large ^ ^ ^ s ^f 'L^^v^^ ^^ 

number of flower-bearing spurs. The &■ - -W_ c 

spur growth of the current year was °~~ <£=}--£ 

cut from the parent spur just at the Fig. 2. preparation of spur previous 

base of the ring of bud scales pro- TO WEIGHING 

- 1 . 1 • 1 j.1 The point C just below the ring of bud-scaie 

teCtlllg the bud from Which the CUr- sears, B, indicates the point at which the present 

, , /n \ year's growth, A, is cut from the preceding year's 

rent years growth Came (fig. 2). growth, DE. The fruits are removed before the 

_., . . .. . . 1 spur is weighed. (Slightly reduced) 

The spurs were weighed in a turgid 

condition. The weights were taken early in the season, and any growth 
arising from a lateral bud on the current season's spur was removed 
before weighing. 

All flower-bearing spurs found on a given limb were considered; the 
setting and the non-setting spurs were therefore produced on the same 
parent branch. The data given in table 20 are representative of the 
weights of setting and of non-setting spurs. 

According to the table, the setting spurs on a given branch are heavier 
than the non-setting spurs on the same branch in all cases. It should be 
noted that the average weight of spurs may be greater on one branch 
than on others. More specific observations regarding this point are 
discussed later (page 73). 



68 Bulletin 393 

TABLE 20. Weights of Setting and of Non-setting Flower-bearing Spurs 





Branch 


Setting spurs 


Non-setting spurs 


Variety 


Num- 
ber of 

spurs 


Total 
weight 
(grams) 


Average 
weight 

(grams) 


Num- 
ber of 

spurs 


Total 
weight 

(grams) 


Average 
weight 
(grams) 


Baldwin 


1 
2 

3 
4 
5 
6 

1 
2 


97 

66 

46 

139 

4" 
42 
37 
34 
10 
30 
48 


174.46 

210.50 
128.64 

383 60 
109.94 
105.00 
107 -75 
59-50 

8 [2 

128.24 
102 74 


1 80 


115 

47 
24 

1 12 
42 
16 
81 

175 
42 
58 
48 


179 56 
91.87 
58.42 

1 62 . 40 
55 02 
24 96 

137 93 

134- 75 
23.24 

180.35 
91.92 


1 .56 


Tompkins King. . . . 

Fallawater 

Rhode Island 

Westfield . . . 


3 
2 
2 
2 
2 
2 
1 

4 
2 


19 
80 
76 
39 
50 
91 
75 
81 
27 
14 


1-95 
2-43 

1 45 
1 3i 
1.56 
1 70 
0.77 

55 
3ii 

1 .92 


Total 




595 


1,518.49 


2-55 


760 


1,140.42 


1.50 



Set of jruit on spurs of different weights 

The flower -bearing spurs from a Fallawater branch were classified, 
according to their weights, as heavy, medium, and light. The average 
weight of each lot is given in table 21, together with the percentage of 
spurs that produced fruit: 

TABLE 21. Set of Friii on Sih rs of Different Weights 



Number of spurs 


Average 
weight 
(grams) 


Percentage 
with 

fruit 


18 


4 53 
2-37 

1 .21 


61 1 


18 


25-5 
16 6 


is 







The' heaviest spurs produced the most fruit, and the lightest produced 
the least. These data alone arc insufficient to establish the relation between 
set of fruit and vigor of spur, but they lend additional support to the 
facts presented in tables 20 and 22. 

1 1 'eights of spurs holding fruits for varying lengths of time 

The weights of spurs that lost all fruit at the first drop, of those 
that held fruit until the June drop, and of those that held fruit after the 



Abscission of Flowers and Fruits of the Apple 



69 



June drop, were obtained in the case of a large limb taken from a Baldwin 
tree in July, 19 15. The scars on the spurs that had lost fruits during the 
June drop were easily distinguishable from the smaller scars of the flowers 
and fruits that had been lost earlier. The data are recorded in table 22: 



TABLE 22. Weights of Spurs Holding Fruits for Varying Lengths of Time 



Time spur held fruit 



Number 

of 

spurs 



Total 
weight 
(grams) 



Average 
weight 
(grams) 



Until first drop . 
Until June drop 
After June drop 



30 
28 
30 



88.12 

92.23 

128.23 



2.94 

3 29 
4.27 



The spurs that finally set fruit are heavier than the others. Those 
that hold fruit until the June drop weigh more than those that lose all 
fruit during the first few weeks. 



Relation between weight, or vigor, of the fruit-bearing spur, and number of 

fruits borne by it 

In several cases the fruit-bearing spurs from a given limb were divided 
into two lots. One lot consisted of spurs that produced one fruit, the 
other of spurs that produced two fruits. The average weight of each lot 
was obtained. The figures are recorded in table 23, and show that spurs 
bearing but one fruit are not so heavy as those bearing two fruits : 

TABLE 23. Relation between Weight of the Spur and Number of Fruits 

Borne by It 





Branch 


Spurs with one fruit 


Spurs with two fruits 


Variety 


Number 

of 

spurs 


Average 
weight 
(grams) 


Number 

of 

spurs 


Average 
weight 
(grams) 


Baldwin 

Baldwin 


1 
2 


25 
60 


1 .60 

3.08 


25 
39 


1.84 
3.62 



The relation between the vigor, or weight, of a spur and its tendency 
to produce more than one fruit is further emphasized by the data in 
table 24. The spurs included in the strong lot had much larger leaves, 
and more leaves to the spur, than those in the weak lot. All spurs were 
taken from the same branch. The table shows that the strong lot con- 
tained more spurs with two fruits than did the weak lot. 



70 Bulletin 393 

TABLE 24. Set of Fruit on Strong and on Weak Spurs 





Strong spurs 


Weak spurs 


Variety 


Number 

of 

spurs 


Percentage 
with two 

fruits 


Number 

of 

spurs 


Percentage 

with two 

fruits 


Baldwin 


94 


34 


33 


I5- 2 







The fact that fruit-setting spurs are heavier on the average than those 
that do not set fruit, suggests that the presence of the fruit on the spur 
may in itself be a stimulant to increase the weight of the spur. It is 
probable that the food which is translocated to the developing fruit accu- 
mulates just beneath the fruit stem, and in that way increases the weight 
of the fruit-bearing spur. Such an accumulation of food, however, is 
usually not apparent until after the fruits have attained considerable 
size. The presence of a fruit on a relatively weak spur does not materi- 
ally increase its weight early in the season, nor does the absence of a fruit 
from a vigorous spur put it in the weak class. The weight of the spur 
is closely correlated with other conditions, as may be seen from the 
following paragraphs. 



RELATION BETWEEN WEIGHT OF THE SPUR AND NUMBER OF FLOWERS TO 

THE SPUR 

As previously shown, spurs with many flowers have a greater tendency 
to set fruit than those with a small number of flowers. The question 
whether there is a relation between the number of flowers on the spur 
and its weight, naturally suggests itself. Representative data regarding 
this question are contained in table 25. The figures are based on a con- 



TABLE 25. 



Relation between Weight of the Spur and Number of Flow t ers 
on It 



Flowers to the spur 


Number 

of 

spurs 


Total 
weight 
(grams) 


Average 
weight 
(grams) 


4 


6 

19 

18 


10.58 

51 -77 
60.41 


1 .76 
2.72 
3 -36 


S 


6 





sideration of spurs on a limb from a Maiden Blush tree. It is seen that 
spurs with many flowers are usually heavier than those with few flowers. 



Abscission of Flowers and Fruits of the Apple 



7i 



relation between weight of the spur and length of the previous 

season's growth 

Data are presented in tables 18 and 19 (pages 65 and 66) indicating 
that spurs making a relatively short growth during the season previous 
to the one in which they bear flowers are less likely to set fruit than spurs 
making a longer growth. Is there any relation between such length growth 
and the weight of the new spur growth arising from the terminal bud ? 

In a study of this question the flower-bearing spurs from several Bald- 
win limbs were divided into two lots. One lot consisted of spurs from 
buds terminating more than one centimeter of 191 5 growth; in the other 
lot, the spurs were from buds terminating less than one centimeter of 
19 1 5 growth. The total weight of each lot and the average weight of 
the spurs are given in table 26: 



TABLE 26. Relation between Weight of the Spur and Length of the 
Previous Season's Growth 



Variety 


Branch 


Spurs making more than 1 
centimeter growth during 
previous season 


Spurs making less than 1 
centimeter growth during 
previous season 


Num- 
ber of 
spurs 


Total 
weight 
(grams) 


Average 
weight 
(grams) 


Num- 
ber of 
spurs 


Total 
weight 
(grams) 


Average 
weight 
(grams) 


Baldwin . . . 


1 
2 
3 
4 


75 

15 

10 

129 


199.6 

33-5 

16.8 

402.0 


2.66 

2.2^ 
1^68 
3.12 


59 

53 

27 

122 


83.1 

94 

29.8 

143.0 


1. 41 

1 77 
1 10 


Baldwin . . . 


Baldwin 


Baldwin. . . 


1. 17 




Total 


229 


651-9 


2.85 


261 


349-9 


1-34 


1 



The figures indicate that spurs making a relatively long growth during 
the preceding year will produce heavier and more vigorous buds in the 
following year than those making a short growth. That the spurs arising 
from buds terminating several centimeters of a given season's growth 
are more vigorous than spurs arising from buds on short spur-growth, 
may be observed even before the individual flower buds open (fig. 3). 

It should not be assumed, however, that vigorous buds are produced 
only on relatively long growth and that spurs making a short growth 
are always weak. Cases in which the reverse conditions obtain are occa- 
sionally found. Nevertheless, the length of spur growth produced during 
the previous season forms a very convenient and satisfactory guide to 
the vigor of a spur, and the best criterion for a probable set is found in 
this character. 



I'i I LETIN 393 




The advantages of having a basis for estimating the probable set are 
numerous. For example, plant breeders working on the apple might 

save considerable time and secure a higher 
percentage of set if they confined their 
work of cross-pollination to the vigorous, 
many-flowered spurs that have made sev- 
eral centimeters growth during the preced- 
ing season. 

RELATION BETWEEN WEIGHT OF THE NEW 

SPUR GROWTH AND DIAMETER OF THE 

CONDUCTING TISSUE 

' In cutting off the spur growth just pre- 
vious to weighing, it was observed that the 
diameter of the cylinder of conducting 
tissue varied between i and 2.5 millimeters 
(fig. 4). Closer inspection showed that the 
spurs with conducting tissue of large di- 
ameter had a greater leaf surface than 
spurs with conducting 
tissue of smaller di- 
ameter. The weights 
of new spur growth, 
together with the di- 
ameters of the con- 
ducting tissue of the 
spurs, are given in 
table 2 7 . The material 
used was from a large 
limb on a Tompkins King tree. All flower-bearing 
spurs on the limb were considered. 

The weights of the spurs show a relation to the 
diameters of the cylinders of conducting tissue. 
The smaller the conducting tissue is in diameter, 
the lighter is the new spur growth. 

It should be noted that spurs with conducting 
tissue of large diameter are sometimes produced 
from buds that were terminal to less than one cen- 
timeter of spur growth. In all such cases, however, 
the spurs are large, in accordance with the preced- 
ing data. Likewise, when spurs show relatively small conducting-tissue 
cylinders, they are usually light in weight even tho they arise from buds 
terminal to several centimeters growth. 




Fig. 3. LEAVES AND flowers on 
SPURS OF DIFFERENT VIGOR 

Lower figure, a typical vigorous spur of 
the variety Tompkins King; upper figure, 
a spur below medium in vigor, of the same 
variety. The spurs were obtained just 
before the flower buds opened. The num- 
ber of flowers (A, A'), the number and 
size of the leaves, and the length of the 
Qg year's spur growth (B, B'), 
may be compared. ( 3 natural size) 




—c 




Fig. 4. CONDUCTING 
CYLINDERS IN SPURS 
OF DIFFERENT VIGOR 

Cross section of a vigor- 
ous spur, below, and of a 
moderately vigorous spur 
above. A, pith; B, xylem 
(conducting tissue); C, cor- 
tex. The section was ob- 
tained just above the ring 
of scars. Outline from ca- 
mera lucida drawing. X 6 



Abscission of Flowers and Fruits of the Apple 



73 



TABLE 27. Relation between Diameter of Conducting Tissue and Weight 

of Spur 



Relative diameter of conducting tissue 



Number 

of 

spurs 



Total 
weight 
(grams) 



Average 
weight 
(grams) 



Small (1-1.5 mm.). . 
Medium (1.6-2 mm.) 
Large (2.1-2.5 mm.) . 



74 
112 

39 



no. 7 
276.4 
12745 



1.50 
2.47 
3-27 



RELATION BETWEEN DIAMETER OF CONDUCTING TISSUE AND WEIGHT OF 

SPURS, FROM LIMBS HAVING A LIGHT BLOOM AND FROM 

THOSE HAVING A FULL BLOOM 

As previously shown, the percentage of fruit set on limbs with rela- 
tively few flower-bearing spurs is greater than on limbs with an abundant 
bloom. It has been seen that heavy spurs have a greater tendency to 
set fruit than weak spurs, and that there is a relation between the weight 
of the spur and the diameter of the conducting cylinder in the spur. Are 
the spurs on limbs with a light bloom, heavier and more vigorous than 
the spurs on limbs with a full bloom? If so, is the conducting tissue of 
greater diameter in the former spurs than in the latter? These questions 
are answered by the data in table 28. Lot 1 consisted of all flower -bearing 
spurs from a limb on a Baldwin tree, and lot 2 of spurs from limbs on 
an Autumn Strawberry tree. Only twenty-five spurs from the limbs with 
a full bloom, and twenty-five from the ones with a light bloom, were 
considered in the latter case. 

TABLE 28. Relation between Diameter of Conducting Tissue and Weight 
of Spurs, from Limbs Having a Light Bloom and from Those Having 
a Heavy Bloom 



Lot 


Relative diameter 
of conducting tissue 


Spurs from limbs with 
a light bloom 


Spurs from limbs with 
a heavy bloom 




Number 

of 

spurs 


Average 
weight 
(grams) 


Number 

of 

spurs 


Average 
weight 
(grams) 




f Small (1— 1.5 mm.) . . 


7 
34 
14 


2 .06 

3 09 
4.01 


49 
56 
20 


1.50 

2-37 
3.10 


1 


\ Medium (1 .6-2 mm.) 

( Large (2.1-2.5 mm.) 

Total 




55 


3.20 


125 


2 16 










f Small . . 


5 
16 

4 


1.84 
2-53 
3 -38 


7 
11 

7 


1-44 
239 
2.63 


2 


■j Medium 




[ Large 




Total 




25 


2-53 


25 


2.19 







74 Bulletin 393 

The figures shew that limbs with a light bloom have heavier spurs 
than limbs with a heavy bloom, and that spurs with conducting tissue 
of a given .diameter taken from the former limbs weigh more than spurs 
with conducting tissue of the same diameter taken from the latter limbs. 
The leaves produced on spurs from limbs with a light bloom have a notice- 
ably greater area than those produced on spurs which have conducting 
tissue of equal diameter but which were taken from limbs with a heavy 
bloom. The average leaf surface of several equally vigorous spurs ob- 
tained from these two sources was 125.34 and 86.51 square centimeters, 
respectively. The leaf area was measured by a planimeter. 

RELATION BETWEEN WATER SUPPLY, LEAF AREA, AND PUSHING OF BUDS 

It is generally understood that an abundant supply of water is a factor 
in producing large leaves. This was demonstrated by the following simple 
experiment. A number of dormant apple twigs were divided into two 
similar lots. The cut ends of the twigs were placed in beakers containing 
water. In one lot the cuts were renewed every few days and in the other 
lot they were renewed only seldom. The leaves of the former twigs were 
noticeably larger than those of the latter. This difference in size may be 
ascribed to the more abundant water supply obtained by the leaves on 
the twigs that had their cut ends frequently renewed. 

A more elaborate experiment, which involved the forcing of water into 
the cut ends of the twigs, likewise indicated that there was a relation 
between the leaf surface and the water supply. The details of the appa- 
ratus used for this demonstration are shown in fig. 5. Tompkins King 
branches from three to four years old and approximately one meter long 
were used. The leaves on the twigs that had water forced into their 
bases were distinctly larger than those on untreated twigs. 

This experiment, which was carried on in duplicate and which was 
repeated several times, yielded other results that may be of interest at 
this point. The buds on the check twigs, which were standing in a jar 
of water, opened about a week before the buds on the twigs that received 
their water supply under pressure. The first buds to open on the latter 
twigs were the small ones on relatively weak spurs. The first vigorous 
buds to push were those nearest the tops of the twigs. Droplets of sticky 
material oozed from all of the larger buds, which were found at the end 
of several centimeters of the previous season's growth. Similar exuda- 
tions were observed on less vigorous buds produced on spurs arising near 
the bases of the twigs. 

Apparently the delay in the pushing of buds was caused by excessive 
water pressure. The resistance encountered by the water passing thru 



Abscission of Flowers and Fruits of the Apple 



75 



a meter of conducting 
tissue of the twig was 
apparently sufficient to 
reduce the pressure to 
a point at which bud- 
pushing could occur; 
hence, the first vigor- 
ous buds to open were 
those nearest the tops 
of the twigs. Weak 
spurs apparently- 
offered greater resist- 
ance to the passage of 
water; hence, they 
pushed first because 
they were not over- 
supplied with water. 

It has been shown 
previously that vigor- 
ous, heavy spurs are 
usually provided with 
conducting tissue of 
comparatively large 
diameter. This experi- 
ment shows that the 
large, plump buds 
which produce the 
heavy spurs are more 
abundantly supplied 
with water than the 
smaller buds. 

The difference in leaf 
area between the vig- 
orous and the weak 
spurs is probably due, 
in part at least, to the 
difference in water sup- 
ply, or, more accu- 
rately, sap supply. 
The vigorous spurs 
have larger leaves 
than the weak spurs 





-G 



H 



Fig. s. 



APPARATUS FOR FORCING WATER INTO THE ENDS 
OF TWIGS 

The pressure is supplied by a column of water three meters long. 
This column is maintained at approximately the same level by the 
water in the funnel. A, which is connected to the tube, C, by the union 
at B. The tube passes thru the cork, F. This cork is also provided 
with holes for the twigs, D. The twigs are from three to four years 
old and about one meter long. After these twigs and the tube have 
been inserted, the bottle, G, is filled with water. The cork is then 
flooded with warm paraffin. After this has become firm the pressure 
is applied. Check twigs are placed in the bottle H 



76 Bulletin 393 

because they have a greater diameter of conducting tissue and hence can 
obtain more sap. 

It has been seen that the leaf area for spurs which have a conducting 
tissue of a given diameter and which were taken from limbs producing 
many flowers, is less than that for spurs with the same diameter of con- 
ducting tissue but taken from limbs producing few flowers. If the size of 
the leaves is an indication of the supply of sap that reaches the spur, it 
must be assumed that the former spurs are not so abundantly supplied 
as the latter even tho they have conducting tissue of the same diameter. 
It probably requires greater sap pressure to expand mixed buds, which 
contain both flowers and leaves, than is needed to push leaf buds. More- 
over, the petals of the flowers will transpire considerable moisture. It 
seems reasonable, therefore, to assume that limbs producing a heavy 
bloom will supply less sap to the individual spur than similar limbs which 
produce a light bloom. The spurs from the former limbs are not so likely 
to set fruit as those from the latter limbs. Can this be due to an inade- 
quate supply of sap ? 

RELATION BETWEEN AMOUNT OF LATERAL GROWTH FROM THE FLOWER- 
BEARING SPUR, AND FRUITFULNESS OF THE SPUR 

The elongation of a spur that is producing flowers is dependent on the 
pushing of at least one lateral bud found on the current season's spur 
growth (fig. 1 , page 51). In a few spurs the setting of a fruit inhibits the for- 
mation of a lateral bud. In some cases lateral buds are formed, but they 
do not push until the following year; in other cases, as much as twenty- 
five centimeters lateral growth' is produced by the f raiting spur. All 
gradations between these extremes are found. The lateral growth may 
begin even before the flowers have opened, and by the time the fruit 
sets such growth may be several centimeters long. Observations here 
showed that fruit-setting on spurs that had made from five to ten centi- 
meters of lateral growth was not uncommon. In fact it appeared that 
only a relatively small proportion of such spurs lost their fruit. 

The amount of lateral growth produced by setting and by non-setting 
spurs derived from the same limb was recorded in several cases. Data 
for a Baldwin limb are given in table 29. It is seen that fruit is borne on 
spurs that produce much lateral growth as well as on those that produce 
little growth. The average weight of the lateral growth is greater in the 
spurs that bear fruit than in those that lose their fruit. 

In other cases, the lateral growth produced by spurs taken from limbs 
that bore many fruits and from similar limbs that bore few fruits, was 



Abscission of Flowers and Fruits of the Apple 



77 



TABLE 29. Lateral Spur Growth Produced by Setting and by Non-setting 
Spurs from a Baldwin Limb 



Amount of lateral growth 


Produced by 
setting spurs 


Produced by 
non -setting spurs 


No growth 


6 
20 
20 

5 

1 

1 .35 grams 

2 . 39 grams 




2 leaves 


13 

14 

5 




3 leaves 


4 leaves 


5 centimeters 


Average weight of lateral growth 


. 79 gram 
1 .31 grams 


Average weight of spurs minus lateral growth .... 



carefully examined. The results obtained with a pair of similar limbs 
from a Strawberry tree are recorded in table 30. One hundred of the 
largest spurs from each limb are considered. 



TABLE 30. Lateral Growth Produced by Large Flower-bearing Spurs, 
from Limbs Setting Few and from Those Setting Many Fruits 



Amount of lateral growth 



Produced by 
spurs from 

limbs setting 
few fruits 



Produced by 
spurs from 
limbs setting 
many fruits 



2 leaves 

3 leaves 

o. 5-5 centimeters 

5. 1-10 centimeters 

10. 1-20 centimeters 

Over 20 centimeters 

Average weight of lateral growth 



24 
42 
29 

5 
o 
o 
1 .91 grams 



12 

23 

34 

7 

10 

14 

3 



70 grams 



According to the table, the spurs from the fruitful branches have a 
tendency to produce more lateral growth than those from the less fruitful 
limbs. The average weight of the lateral growth produced by the former 
spurs is almost double that produced by the latter. 

These figures indicate that fruit-setting is not opposed by vegetative 
activity as manifested by the amount of lateral spur growth. On the 
contrary, they suggest that the conditions which favor such growth are 
likewise favorable for the setting of fruit. 

One of the essential conditions for the forcing of the lateral buds 
is an abundant supply of sap. It is well known that heavy pruning of an 
apple tree during the dormant season stimulates the production of vigor- 
ous shoots from the remaining growing points. Such pruning disturbs 
the equilibrium between the top and the root systems, and as a result 
there is an abundant supply of food and water for vigorous top growth. 



78 Bulletin 393 

It should also be pointed out that the lateral buds on many flower-bearing 
spurs can be forced into growth by severe pruning of the branch that 
produces the spurs. It seems reasonable, therefore, to assume that such 
lateral spur growth is an indication of an abundant supply of sap. 



RELATION BETWEEN SAP SUPPLY AND FRUIT SETTING 

Several of the observations previously recorded have suggested that 
an adequate supply of sap to the individual spur is an important factor 
in the setting of fruit. The object of the following experiments was to 
determine whether the percentage of spurs that set fruit could be increased 
by increasing the sap supply, or decreased by reducing the sap supply, to 
the individual spurs. 

In the spring of 19 16, large limbs, which were approximately five centi- 
meters in diameter at their bases and which had a full bloom, were selected 
in pairs. The members of such pairs either formed the arms of a Y or 
arose within a foot of each other from the same parent branch. It was 
necessary to have the limbs of a given pair as nearly alike as possible 
in vigor, exposure, bloom, and size, and for this reason the selection of 
suitable pairs was no easy task. 

In several cases one limb of a pair was sawed halfway thru near its 
base, and the second limb was left untreated or was pruned lightly by 
cutting out entire twigs containing both weak and vigorous buds. In 
other cases one limb was left unpruned and not sawed at its base, while 
the second limb had at least half the total number of branches removed. 
The object of sawing the branches at the base was to diminish the normal 
sap supply to the spurs on the limbs so treated. The aim of the severe 
pruning was to increase the flow of sap to the individual buds. The 
treatments were given just before the flowers opened. The results are 
recorded in table 3 1 : 



TABLE 31. 



Percentage ok Flower-bearing Spurs Setting Fruit on Limhs with 
1 m kkased and on those with diminished sap supply 



Lot 


Variety 


Limbs with normal or increased 
sap supply 


Limbs with normal or diminished 
sap supply 


Treat- 
ment of 
limb* 


Num- 
ber of 
spurs 


Num- 
ber set 


Per- 
centage 
set 


Treat- 
ment of 
limb* 


Num- 
ber of 
spurs 


Num- 
ber set 


Per- 
centage 
set 


1 
2 


Tompkins King 

Tompkins King 


2 
3 

2 
3 

4 
4 

2 


71 
71 
350 
767 
112 
177 
46 
119 


14 
22 
131 
226 
36 
61 
40 
82 


10.7 
310 
374 
20-5 
32.1 
34-5 
87.0 
68.9 


4 
1 

4 
4 
1 
1 
1 
4 


166 

T II 
682 

1.445 
143 

184 
45 

145 


15 
25 
139 
344 
3i 
38 
19 
77 


9 

20 
23 

21 
20 
42 

S3 



5 
4 

8 






5 




7 
6 


6 




7 






8 













♦Treatments: i, treated limb sawed at base; 2, treated limb severely pruned; 3, treated limb slightly 
pruned; 4, limbs untreated. 



/ 



Abscission of Flowers and Fruits of the Apple 



70 






In all cases the limbs that received relatively little sap had a smaller 
percentage of fruit-setting spurs than those receiving an abundant supply 
of sap. In a case not recorded in the table, members of a pair of branches 
on a Strawberry tree were left untreated. One arm had 1064 flower- 
bearing spurs, and the other arm had 1155. The percentage of spurs 
setting fruit was 22 for the former and 22.2 for the latter. The untreated 
limbs in lots 3 and 4, table 31, produced fruit on 20.4 and 23.8 per cent, 
respectively, of their spurs. These figures would seem to indicate that 
the range of variation in the percentage set is only slight when large 
numbers of spurs are involved. 

As previously shown, the lateral growth produced by a flower-bearing 
spur may be taken as an index to the sap supply to that spur. In order 
to determine whether the treatments given had the desired effect of 
increasing or decreasing the sap supply, the lateral spur growth was 
carefully examined in each case. The analyses of the lateral growth 
produced by fifty of the largest flower-bearing spurs from a pruned branch 
and an equal number from an unpruned branch of a Strawberry tree 
are recorded in table 3 2 : 



TABLE 32. Lateral Growth Produced by Flower-bearing Spurs from a Pruned 
Branch and from an Unpruned Branch 



Amount of lateral growth 



Produced by 

spurs from 

pruned branch 11 



Produced by 

spurs from 

unpruned branch! 



2 leaves 

3 leaves 

0.5-5 centimeters 

5. 1-10 centimeters 

Over 10 centimeters 

Average weight of lateral growth 



5 
6 

31 
4 
4 
2 . 68 grams 



17 
19 
10 

3 
1 

1 .90 grams 



* 37-4 P er cen t °f the flower-bearing spurs produced fruit, 
t 20.4 per cent of the flower-bearing spurs produced fruit. 



The spurs from the pruned branch made a more vigorous lateral growth 
than those from the unpruned branch. This indicates that the pruning 
actually increased the amount of sap available for each spur on the treated 
branch. The observations made in the remaining cases showed that the 
limbs which set most fruit to the hundred spurs also produced the most 
vigorous lateral spur growth. 

The percentages of large and of small spurs setting fruit on the limbs 
that received relatively little sap to the spur, and on those that received 
relatively much sap to the spur, are recorded in table 33. The spurs 
were classed as large if they were produced from buds that were terminal 



8o 



Bulletin 393 



to one or more centimeters of the previous season's spur growth; if the 
spur growth was less than one centimeter, the spurs were classed as small. 

TABLE 33. Percentage of Large and of Small Spurs Setting Fruit on Limbs 
with Diminished and on Those with Increased Sap Supply 





Variety 


Large spurs 


Small spurs 


Lot 


Diminished 
sap supply, 
percent- 
age set 


Increased 

sap 
supply, 
percent- 
age set 


Per- 
centage 
gain 


Diminished 
sap supply, 
percent- 
age set 


Increased 

sap 
supply, 
percent- 
age set 


Per- 
centage 
gain 


1 
2 

3 
4 
5 
6 

7 
8 


Tompkins King . . 
Tompkins King . . 

Strawberry 

Strawberry 

Baldwin 

Baldwin 

Baldwin 

Baldwin 


25.0 
28.6 
47- 1 
37- 1 
37-3 
38.0 

48.3 
82.1 


26. 1 
50.0 
50.7 
51-9 
50.0 
62.0 
88.0 
85.1 


1 . 1 
21.4 

36 
14.8 
12.7 
24.0 

39-7 
30 


6.8 
22 . 1 
18.4 
11 5 
7 9 
9 7 
31.2 

13 1 


16.6 
28.6 
22 .0 

3i 1 
20.6 

25-7 
84.6 
48.1 


9.8 

65 

3 6 

19.6 

12.7 
16.0 

53 4 
35 



More fruit was produced on the large spurs than on the small spurs, 
as would be expected from previously recorded observations. The small 
spurs, as well as the large ones, are benefited by an increased supply 
of sap, as is indicated by the percentage gain. 

The term sap, as used in the preceding paragraphs, has reference 
primarily to the watery solution taken up by the roots. No doubt some 
of the organic food stored in the roots, and in the trunk and the main 
limbs of the tree, would find its way into this solution before it reached 
the spur. It would be difficult to state definitely which was the more 
beneficial to the set of fruit — the water or the food material that it 
contained in solution. The fact that the vigorous spurs have a larger 
number of leaves and flowers than the weaker spurs, in itself suggests 
that the buds in which they were formed were well supplied with organic 
food. Miiller-Thurgau (1898) has shown that many fruits are borne 
on limbs that have been girdled, while untreated limbs on the same tree 
with equally heavy blooms set relatively few fruits. Chandler (1913) 
has demonstrated that the sap derived from the cortex and the bark 
of girdled apple twigs is much denser than sap from similar limbs receiving 
no treatment. Gourley (19 15) shows that more food is stored in fruiting 
than in non-fruiting spurs. There can be little doubt that an abundance 
of stored food is one of the factors favoring the setting of fruit. On the 
other hand, it must be borne in mind that heavy spurs usually have 
a large diameter of conducting tissue, which insures a good sap supply. 
Furthermore, the observations recorded above indicate that an abundant 



Abscission of Flowers and Fruits of the Apple 8i 

supply of sap to spurs inadequately provided with storage tissue increases 
the ability of such spurs to set fruit. 

FRUIT SETTING AS INFLUENCED BY VARYING AMOUNTS OF LEAF SURFACE 
ON THE FLOWER-BEARING SPUR 

As previously shown, limbs with small leaves have a smaller proportion 
of fruitful spurs than similar limbs with large leaves. The area of the 
leaf surface seems to be closely correlated with the vigor, or weight, of 
the spur, which in turn shows a relation to the diameter of the cylinder 
of conducting tissue thru which the sap reaches the developing spur. 
The leaves might have several effects: they might assist in drawing water 
to the spur — the "pulling power of transpiration"; they might provide 
increased nourishment for the developing tissue; , they might prove 
detrimental during conditions favoring incipient drying, by actually 
withdrawing moisture from the young flower or fruit. (Chandler, 191 5). 
In order to gain some information regarding the influence of the bud 
leaves on the setting of fruit, the following experiments were carried out: 

In the first experiment, a number of pairs of similarly located and 
equally vigorous spurs were selected. The vigor of the spurs was 
determined by the amount of leaf surface, and also by noting the length 
of the previous season's growth. The spurs of each pair were taken 
from the same parent branch and from points within a few inches of 
each other. Vigorous spurs only were selected because previous obser- 
vations had shown that such spurs have the greatest tendency to set 
fruit. The importance of having spurs of similar location and vigor is 
obvious. 

One spur of each pair was entirely defoliated, while the other served 
as a check, receiving no treatment. The leaves on the former were 
removed just before the blossoms opened in the spring of 1916. The set 
of fruit on the spurs was determined during the latter part of August. 
Unfortunately, many pairs had to be discarded because of aphid injury. 
Only healthy spurs were considered. The data are recorded in table 34. 

The figures indicate that some of the defoliated spurs bear fruit, but 
the percentage of these is very much less than in the case of normal spurs. 
The high percentage of fruitful spurs recorded for the latter class reflects 
the influence of vigor. 

The object of the next experiment was to determine the effect of partial 
and of complete defoliation of flower-bearing spurs on the setting of 
fruit. Several lots, each consisting of three similarly located and equally 
vigorous spurs, were selected. As a rule, vigorous spurs have from seven 
to ten first, or bud, leaves. One spur in each lot served as a check; the 



82 Bulletin 393 

TABLE 34. Percentage of Normal and of Defoliated Spurs Bearing Fruit 



Variety and 
tree 


Normal spurs 


Defoliated spurs 


Total 
number 


Number 
set 


Percent- 
age set 


Total 
number 


Number 
set 


Percent- 
age set 


Baldwin, 1 

Baldwin, 2 

Baldwin, 3 


16 
1 1 

32 


14 
11 

23 


87-5 
100. 

71 9 


16 
1 1 

32 


6 
6 

12 


37-5 
54-5 
37-5 


Total 

Tompkins King, 1 
Tompkins King, 2 . . 
Tompkins King, 3 . . 


59 

42 
52 
43 


48 

23 
19 
23 


81 .4 

54-8 
36.5 
53-5 


59 

42 
52 
43 


24 

2 

5 
10 


40.7 

4.8 
9.6 

23 3 


Total 


137 


65 


47-4 


137 


17 


12.4 



second spur had all but two leaves removed; the third spur was entirely 
defoliated. The defoliation was done before the flowers opened in the 
spring of 1916. The set of fruit was determined during late August. 
Again many spurs were infested with aphids and had to be discarded. 
The data are recorded in table 3 5 : 



TABLE 35. 



Percentage of Normal, of Partially Defoliated, and of Com- 
pletely Defoliated Spurs Setting Fruit 





Normal spurs 


Spurs with all but 
two leaves removed 


Defoliated spurs 


Variety- 


Total 
num- 
ber 


Num- 
ber 

set 


Per- 
cent- 
age set 


Total 
num- 
ber 


Num- 
ber 
set 


Per- 
cent- 
age set 


Total 

num- 
ber 


Num- 
ber 
set 


Per- 
cent- 
age set 


Baldwin 

Tompkins King 


32 
5i 


23 
19 


71.9 
37-3 


32 
52 


22 
18 


68.8 
34 -6 


32 
52 


12 
5 


37-5 
9.6 


Total 


83 


42 


50.6 8a 


4" 


47.6 


84 


17 


20.2 











The figures show that spurs with two leaves set approximately as 
well as spurs with all leaves. The presence of a small amount of leaf 
surface apparently offsets the harmful effects of entire defoliation. 

Many spurs set more than one fruit. The percentage of such spurs 
in defoliated and in check lots is given in table 36. The normal spurs, 
as might be expected, are more likely to produce two fruits than are defoli- 
ated spurs. The percentage of spurs setting more than one fruit is three 
times as great in the case of the untreated spurs as in the defoliated lot. 



Abscission of Flowers and Fruits of the Apple 83 

TABLE 36. Number of Fruits to the Spur on Normal and on Defoliated Spurs 



Number of fruits to the spur 


Number of spurs with re- 
spective number of fruits 


Normal 
spurs 


Defoliated 
spurs 


1 


35 

19 

4 

39-7 




2 


3 


3 


Percentage of spurs setting more than one fruit .... 


12.5 



These results are interesting because they show that a small leaf surface 
in itself, such as is found on spurs on weak limbs or on those with a heavy 
bloom, is not accountable for a poor set of fruit. The data at hand do 
not afford an adequate explanation for the results obtained. On the 
basis of observations and experiments presented later, however, it seems 
reasonable to assume that the leaves favor fruit -setting on vigorous spurs 
because they assist in drawing sap to the fruit. 



.INFLUENCE OF SUNLIGHT ON THE SETTING OF FRUIT 

In order to learn whether or not a variety is self-sterile, cross-pollination 
is prevented by inclosing the flower spurs in sacks. According to Ewert 
(1907), such treatment subjects the inclosed spurs to unnatural conditions 
which may be unfavorable for the setting of fruit. The object of the 
following experiments was to determine the effect of excluding sunlight 
on the setting of fruit. 

Some vigorous spurs were inclosed in brown opaque paper bags, and 
some in white translucent paper bags. Only the most vigorous spurs 
were inclosed, and for each spur inclosed in a translucent sack a similar 
spur arising from the same parent branch was inclosed in an opaque sack. 
The spurs were sacked in the spring of 191 6, before the clusters of flowers 
had separated. The set of fruit was determined in late summer. Unfor- 
tunately a large number of the sacked spurs had to be discarded because 
of aphid work. The data obtained, however, are very suggestive. They 
are recorded in table 37, in which it is seen that over twice as many spurs 
set fruit in the translucent sacks as in the opaque sacks. 

The following notes may be of interest: On May 17, 19 16, the flowers 
in the opaque bags had white petals, and all flowers in the cluster were 
open; the flowers in the translucent bags had pink petals, and were some- 
what further advanced than the flowers in exposed clusters. The stigmas 



84 



Bulletin 393 



TABLE 37. Set of Fruit on Spurs Inclosed in Opaque Bags and on 
Spurs Inclosed in Translucent Bags 



Variety 


Branch 


Spurs inclosed in 
bags 


opaque 


Spurs inclosed in 
cent bags 


translu- 


Total 

number 


Num- 
ber set 


Percent- 
age set 


Total 
number 


Num- 
ber set 


Percent- 
age set 


Baldwin 

Baldwin 


1 
2 


25 
19 


7 
3 


28.0 
15.8 


25 
19 


11 


44 
73-7 


Total 




44 


10 


22.7 


44 


25 


56.8 



on all inclosed flowers were green; those on exposed flowers had a reddish 
tinge, even before the petals unfolded. The leaves on all the inclosed 
spurs were smaller than those on the exposed spurs. At the time when 
the fruit-setting spurs were counted, it was observed that there was a 
tendency for fruit in the translucent sacks to attain the June-drop size 
before it fell, whereas in the opaque sacks the fruit fell when very 
small. All the flowers in the experiment were self-pollinated if polli- 
nated at all. 

The figures indicate that exposure to sunlight is an added advantage 
in fruit setting. The results agree with those of Lubimenko (1908), who 
finds that illumination is essential during the early stages of development 
of young fruit. 

Inclosing the spurs in bags inhibits the free circulation of air, and trans- 
piration is probably reduced as a result. The air temperature in the 
brown bags would be higher than that in the white bags on sunny days. 
The diffused light in the translucent sacks would be sufficient for some 
photosynthetic activity, while practically all light is excluded from the 
opaque sacks. The leaves in the former, being exposed to light, would 
probably have greater osmotic properties than those in the dark (Chand- 
ler, 19 1 3). The advantage of having leaves with the greater osmotic 
properties would be that more sap would tend to flow in the direction 
of the spurs which produce such leaves. This sap would be available 
for the setting of fruit. 



RELATION BETWEEN SEED FORMATION AND FRUIT DEVELOPMENT 

It is commonly supposed that the apples which are poorly fertilized 
and which consequently develop few seeds, tend to fall off during the June 
drop. That there is a close relation between seed formation and fruit 
development is shown in the following paragraphs. 



Abscission of Flowers and Fruits of the Apple 



85 



Number of seeds in fruit that sets and in fruit that drops 
The drop apples have fewer seeds on the average than are found in 
the average fruit that remains on the tree, as shown by the representative 
data in table 38: 

TABLE 38. Average Number of Seeds in Fruit That Drops and in Fruit That 

Remains- on the Tree 





Drop fruit 


Attached fruit 


Variety 


Number 
of fruits 


Average 

number of 

seeds to 

the fruit 


Number 
of fruits 


Average 

number of 

seeds to 

the fruit 


Baldwin 

Rhode Island 

Maiden Blush 


48 
66 
65 


3-38 
3-51 
3-94 


47 
29 
66 


4-47 
6-43 
6 28 







The number of seeds found in individual fruits that have fallen and in 
individual fruits taken from the tree are given in table 39. The column 
on the left contains the number of seeds to the fruit. The figures in the 
other columns give the number of fruits showing the respective number 
of seeds. It is seen that many attached fruits have relatively few seeds 
and some drops have a high seed content. This suggests that other factors, 
in addition to fertilization or pollination, are responsible for the set of fruit. 



TABLE 39. Number of Seeds in Fruit That Drops and in Fruit That Remains 

on the Tree 





of seeds to the 
fruit 


Baldwin • 


Rhode Island 


Maiden Blush 




Attached 
fruit 


Drop 

fruit 


Attached 
fruit 


Drop 

fruit 


Attached 
fruit 


Drop 

fruit 


I . 


5 
9 
9 
14 
6 

3 
1 


2 

16 
12 

7 
4 
6 


1 


4 
1 

5 
5 
5 
6 
1 
1 
1 


6 

13 

18 

9 

15 

2 

1 

2 


1 
4 
9 

7 

4 

10 

10 

1 1 

6 

2 



1 

1 


3 


2 


17 


1 


17 


4. . 


8 


5 


6 


6 


7 


7 


3 


8 


4 


9 





































86 



Bulletin 393 



Osterwalder (1907 a) examined the seeds in fruit that had fallen from 
the tree. He found that sixty-five per cent of these contained embryos, 
while about seventy-five per cent of the seeds in the fruit that remained 
on the tree contained embryos. 

Relation between number of seeds and size of fruits 
Muller-Thurgau (1898) has studied the relation between the number of 
seeds and the size of berry in the grape. For eighteen varieties of grapes 
he finds the foil owing averages: 

Weight of flesh of 100 seedless grapes, 42.8 grams 
Weight of flesh of 100 1 -seeded grapes, 144.0 grams 
Weight of flesh of 100 2-seeded grapes, 209.3 grams 
Weight of flesh of 100 3-seeded grapes, 253.9 grams 

He also presents data indicating that a similar relation exists in the case 
of apples and pears, and his results are substantiated by Ewert. The 
general law, that the more are the seeds the larger is the apple, is illus- 
trated by the figures in table 40. These data were obtained in 19 15 from 
trees in the experiment station orchard at Cornell. 



TABLE 40. Number 


of Seeds and Size of 


Fruits 






Maiden Blush 


Baldwin 


Number of seeds to the 

fruit 


Number 
of fruits 


Average 
diameter 
(milli- 
meters) 


Number 
of fruits 


Average 
weight 

(grams) 


1 

2 


2 
16 

27 
10 

5 
6 

3 
2 
2 


8.0 
10.5 
11. 9 
13.2 
14.6 
16.8 
17.7 


2 

4 

5 

11 

5 
9 


2.98 

3 27 
3.60 
4.84 
5-47 
653 


3 

4 

5 

6 

7. . . 


8 


19.8 ' 

19 




9 













This relation, being based on averages, will naturally not cover all 
cases. During preliminary observations, few-seeded apples were found 
which were as large as many-seeded fruits, and not infrequently even 
larger. Further study showed that in a number of cases the relatively 
small fruit with many seeds was associated with a small spur. This sug- 
gested that the vigor of the spur, as determined by its weight, might be 



Abscission of Flowers and Fruits of the Apple 



87 



a factor, together with the number of seeds, in determining the size of 
the fruit. Accordingly, accurate weights of several hundred spurs, 
together with the weight of the fruit borne on these spurs and the number 
of seeds contained in each fruit, were recorded. The weighings were made 
during July of 191 5 and July of 19 16. The data obtained in this way 
are analyzed from several points of view in the following paragraphs. 

Size of fruit constant, number of seeds varying. — -In the cases recorded 
in table 41, the fruits in each lot are approximately constant in weight 
but the number of seeds varies. It should be mentioned that the fruits 
in each lot were produced on the same branch. The branches were 
approximately ten years old and measured about one and one-half centi- 
meters in diameter at their bases. 



TABLE 41. 



Weight of Fruit Constant, Number of Seeds and Weight 
of Spurs Varying 



Lot 



Variety 



Weight 
of fruit 
(grams) 



Number 

of seeds to 

the fruit 



Weight 
of spurs 
(grams) 



Tompkins King 

Tompkins King 
Tompkins King 
Tompkins King 
Rhode Island . . 
Westfield 



97 

45 

09 

75 

05 
40 

86 

28 

33 
31 



If the weights of the spurs that bore the few-seeded fruits are compared 
with the weights of those that bore the many-seeded fruits, it is seen 
that in all cases the vigor was greater in the spurs bearing the few-seeded 
fruits. In other words, the smaller the spur, the greater is the number 
of seeds required to produce a fruit of a given size. 

Weight of spur constant, number of seeds varying.— The weight of spurs 
in each group is approximately constant in the cases recorded in table 42. 
The number of seeds in the fruits borne by these spurs varies. In each 
lot, as before, the spurs were produced on the same parent branch. 



88 



Bulletin 393 



TABLE 42. Weight of Spur Constant, Number of Seeds and Weight 

of Fruit Varying 



Lot 



Variety 



Weight 
of spur 
(grams) 



Number 

of 

seeds 



*3 

15 
16 

17 



Tompkins King 
Tompkins King 
Tompkins King 
Tompkins King 
Tompkins King 
Tompkins King 
Tompkins King 
Tompkins King 

Baldwin 

Baldwin 

Baldwin 

Baldwin 

Baldwin 

Baldwin 

Baldwin 

Westfidd 

Falla water 



2 
5 

4 
7 

2 
5 

3 
6 

2 
5 

3 
5 

3 
6 

3 

7 

3 

5 

3 

7 

3 

5 
8 

9 
11 



Abscission of Flowers and Fruits of the Apple 89 

The data show that when the weight of the spur is constant, the size 
of the fruit varies with the number of seeds. In other words, the size 
of the fruit is determined chiefly by the vigor of the spur and the seed 
content of the fruit. 

Weight of spur constant, number of seeds constant, size of embryo varying. — 
Theoretically, according to one interpretation of the above hypothesis, 
if spurs of approximately equal vigor are chosen which bear fruits con- 
taining the same number of seeds, the fruits borne on these spurs should 
be approximately equal in weight. Or, stated in a different way, if the 
fruits vary in size while the seed number remains the same in each, a 
difference would be found in the vigor of the spurs producing these fruits, 
and furthermore one would expect to find the largest apple, on the most 
vigorous spur. That these theoretical results are not always obtained 
may be seen from the examples in table 43 : 



TABLE 43. Weights of Fruits Having the Same Number of Seeds, 
and Weights of the Spurs That Bear the Fruits 



Lot 



Variety 



Number 

of 

seeds 



Weight 
of fruit 
(grams) 



Weight 
of spur 
(grams) 



Baldwin 

Baldwin 

Tompkins King 



4.28 
3.20 

3-55 
1 .90 



54 
59 



These data seem to disprove the existence of a direct relation between 
size of fruit, vigor of spur, and number of seeds. The emphasis, however, 
is to be placed on seed content rather than mere number of seeds. 

In studying the seeds, one cannot help noticing marked differences 
in the size of the seeds in given fruits. The embryos in the seeds likewise 
show considerable variation. The embryo is readily dissected from the 
seed by placing the seed flatwise between the thumb and the forefinger, 
with the lateral edge upward, cutting the edge with a sharp scalpel, and 
pressing the embryo out of the seed coat. 

In several cases the number of embryos found in the seeds of a given 
fruit and the length of the individual embryo were recorded, along with 
the weight of the fruit and the weight of the spur on which the fruit 
was borne. These data are given in table 44- The figures under the 
column headed Length of embryo show the number of seeds in each fruit 
and the length in millimeters of the embryo in each seed; for example, 



go 



Bulletin 393 



6-5-5 indicates that the fruit contained three seeds, which in turn con- 
tained embryos measuring six, five, and five millimeters, respectively. 
The fruits in the different lots are arranged in order of their weight. The 
weights of the spurs bearing the fruit are also given. The fruits in 
each lot were produced on the same branch. 

TABLE 44. Weight of Fruit, Weight of Spur, and Length of Embryo 







Weight 


Weight 


Length of 


Lot 


Variet y 


of fruit 


of spur 


embryo 






(grams) 


(grams) 


(millimeters) 


1 


Tompkins King 


77 °° 


3.60 


6-5-5 






69 


00 


5 


68 


7-7-5 






68 


25 


6 


12 


7-5-3 






65 


3i 


6 


71 


5-5-5 






52 


20 


2 


45 


7-7-6 


2 


Baldwin 


37 
35 


58 
25 


4 
3 


55 
63 


7-7-7 
7-4-2 










33 


95 


3 


53 


7-5-2 






33 


72 


3 


16 


7-6-6 






3i 


97 


3 


75 


7-3-3 






30 


86 


2 


93 


7-7-3 






30 


11 


3 


85 


6-5-3 






26 


42 


2 


62 


7-6-3 


3 


Baldwin 


42 


84 

«4 


3 


76 


8-7-7-7-6-4-1 
8-7-6-5-3-1-0 




4i 


6 


06 






4i 


71 


3 


14 


8-7-6-6-6-4-2 






4<> 


28 


3 


43 


7-7-7-5-4-4-1 






38 


13 


1 


97 


9-8-7-7-6-3-3 






35 


63 


3 


48 


7-7-7-5-5-1 "I 



The data show that in most cases the size of the fruit can be accounted 
for by taking into consideration the weight of the spur and the length 
of the embryos in the seeds. The fruit with the longest embryos will 
usually be the heaviest if it is borne on the most vigorous spur. A fruit 
may attain a good size on a relatively small spur if its seeds contain large 
embryos. Conversely, a small fruit borne on a large spur is the result 
of a small embryo. 

In this connection it should be noticed that a small spur may produce 
a large fruit, and a large spur a relatively small fruit. These facts afford 
additional evidence to show that the weight of the spur is not markedly 
influenced early in the season by the fruit borne on it. 

That exceptions are found to the general rule is not surprising. One 
could hardly expect that a single measurement would tell all about the 
possibilities of the embryos for fruit formation. Some embryos are 
plumper than others even tho they are of the same length. Some have 



Abscission of Flowers and Fruits of the Apple gi 

different shapes. Furthermore, they vary in color, some being ivory 
white, others yellowish, others hyaline in appearance. All this suggests 
a difference in quality, such as might result from cross-pollination, for 
example. 

Number of seeds and seed value. — As shown above, the seed value as 
expressed by the length of the embryo may vary in the different fruits 
even tho the number of seeds is the same. It is entirely possible that 
a many-seeded fruit may have a seed value which is below the normal 
for that number. It may be equal to, and in some cases even less than, 
the seed value of a fruit with few seeds. Such an assumption is borne 
out by the fact that in a large number of three-seeded Baldwin fruits, 
seventy per cent of the embryos were above medium length — five milli- 
meters — while in many-seeded fruits of the same variety only about 
fifty per cent of the embryos were large. If the ratio of the weight of 
the spur to the weight of the fruit is greater in a few-seeded fruit than 
in a many-seeded fruit borne on a similarly located spur of equal weight, 
one would be justified in assuming that the seed value of the latter fruit 
was below normal. A specific case may be taken for example as follows: 



Number of seeds 



Weight 
of spurs 
(grams) 


Weight 
of fruit 
(grams) 


2.05 


49.1 


2 .OO 


44-3 


2 .OO 


62 . 7 



These spurs were borne on the same twig and they produced their fruits 
under similar external conditions so far as could be seen. Obviously, 
the five-seeded fruit that weighs only 44.3 grams has a seed value below 
normal. This seed value is equivalent to that of a few-seeded fruit. 
There may be found a fruit weighing less than 4g grams which nevertheless 
has a high seed value. Such a fruit, however, would be on a spur weighing 
less than two grams; thus, a fruit with four seeds, weighing 35.5 grams, 
was produced on a spur that weighed one gram. 

It therefore becomes necessary to modify the general statement that 
the size of fruit is proportional to the number of seeds. It would be 
more nearly accurate to say that the vigor of the individual spur and 
the seed value of the individual fruit determine the size of the fruits 
derived from the same limb and borne under otherwise similar conditions. 
This statement includes the prominent part played by the spur, and it 
also emphasizes seed value rather than number of seeds. It is, of course, 
very necessary to choose spurs borne under otherwise similar conditions, 
as is shown later. 



92 Bulletin 393 

Relation between seed value, weight of spur, and set of fruit 

That the vigor, or weight, of the flower-bearing spur is an important 
factor in determining whether the flowers will set fruit, has been suggested 
by data previously recorded. Figures have likewise been presented which 
show that the drop apples contain fewer seeds than the fruit that remains 
on the tree. This indicates that the number of seeds, which presupposes 
effective pollination, likewise plays a part in determining the set of fruit. 

Since, then, the smaller spurs are more likely to lose their fruit than 
the larger, and since the average number of seeds is less in the drops 
than in the setting fruit, it is apparent that most of the few-seeded drops 
were borne on small spurs. 

But, as has been shown, there are many fruits that remain on the tree 
even tho they have few seeds — less in some cases than are found in 
the average fruit that has dropped. According to the statements in 
the preceding paragraph, these few-seeded fruits would have fallen if 
they had been borne on relatively light spurs. Therefore it must be 
assumed that they were produced on vigorous spurs. Since relatively few 
fruits with many seeds are found among the drops, and since there is no 
basis for assuming that the flowers on less vigorous spurs will necessarily 
be poorly pollinated and hence develop few seeds, one might expect to 
find fruit with many seeds on relatively weak as well as on vigorous spurs. 
To account for the drops with many seeds it must be assumed, in order 
to be consistent, that these came from very weak spurs. Then, too, 
they might have a low seed value even tho their seed number is high. 

Stating this hypothesis in other words, few-seeded fruits, or, more 
accurately, fruits with a low seed value, are borne only on the heavier 
spurs, while many-seeded fruits, or those with a high seed value, may 
be borne on relatively Jight as well as on vigorous spurs. 

In order to test this hypothesis, the weights of several hundred spurs, 
together with the weights of the fruits borne on them and the number 
of seeds in each fruit, were obtained during late July and early August. 
The weight of spur includes all of the present season's growth minus the 
lateral growth. The spurs were cut from the twig in the manner previously 
described (page 67). The spurs obtained from each twig or branch were 
divided into two lots, one containing the fruits with a high seed value 
and the other including the fruits with a low seed value. The determina- 
tion of the seed value of a fruit was based on the observations regarding 
the relation between number of seeds, vigor of spur, and size of fruit. 
These observations also afforded the suggestions for the study of the 
relation between number of seeds, size of spur, and set of fruit. The 
results are recorded in table 45 : 



Abscission of Flowers and Fruits of the Apple 



93 



TABLE 45. Weights of Spurs Bearing Fruit with a Low Seed Value and of 
Those Bearing Fruit with a High .Seed Value 



Lot 



Variety 



Fruits with a low 
seed value 



Num- 
ber 
of 
spurs 



Average 
weight of 

spurs 
(grams) 



Average 
weight of 

fruit 
(grams) 



Fruits with a high 
seed value 



Num- 
ber 
of 
spurs 



Average 
weight of 

spurs 
(grams) 



Average 
weight of 

fruit 
(grams) 



I 

2 
3 
4 
5 
6 

7 
8 

9 
10 
11 
12 
13 
H 
15 



Baldwin 

Baldwin 

Baldwin 

Baldwin 

Baldwin 

Fallawater 

Rhode Island. . . 
Tompkins King . 
Tompkins King. 
Tompkins King. 
Tompkins King . 
Tompkins King . 
Tompkins King . 
Tompkins King. 
Westfield 

All varieties 



24 
14 
16 

25 
12 

33 
15 
7 
6 
10 
10 
18 
32 
32 
24 



.46 
•56 
91 
. 12 

■56 
•58 
•33 
95 
49 
44 
.78 

•25 
.92 

•33 
•43 



20.33 

30.94 
33-28 
48.29 
20. 11 
26. 19 
23.89 
26.62 
28.72 
49.29 
65.06 
55-92 
13.80 

1515 
19.19 



17 

8 

27 
19 

8 
16 
13 

3 
7 
5 
5 
10 

19 
20 
20 



278 



3 4i 



197 



2-73 
2-73 
2.64 
3.00 
2.60 
2.46 

4-39 
2.36 
5.02 
2.61 
61 
10 



"5 



90 



46 
39 
34 
56 
23 
35 
31 
3i 
42 
51 
67 
122 
16 
19 
25 



It is seen that in practically all cases the spurs bearing fruits with a 
low seed value are heavier than those bearing fruits with a high seed 
value. In the average of all varieties, the spurs bearing fruits with a 
low seed value are 17.6 per cent heavier than those bearing fruits with 
a high seed value. There is no apparent reason why a vigorous spur 
should not bear fruit with a high seed value, hence it is not surprising that 
individual lots, such as numbers 7 and 9, should show heavier spurs for 
many-seeded than for few-seeded fruits. When the average weight of 
spurs for a lot in which the fruit has a low seed value is approximately 
the same as for the fruit from the same branch with a high seed value, 
the weight of the fruit in the latter case is considerably greater than in 
the former; this is shown by lots 4, 6, 7, 12, and 14. In those cases in 
which the fruits are almost of the same weight for many-seeded and for 
few-seeded lots, such as lots 3, 10, and 11, the spurs in the latter are the 
heavier. 

In table 46 only half of the total number of spurs are considered — 
that half containing the smaller spurs. In this table the differences before 
noted are more marked because of the elimination in each class of the 
half containing the heavy spurs. The smaller spurs bearing fruit with a 
low seed value are 28 per cent heavier than the smaller spurs bearing 
fruit with a high seed value 



94 



Bulletin 393 



TABLE 46. Weights of Smaller Spurs Bearing Fruit with a Low Seed Value 
and of Those Bearing Fruit with a High Seed Value 



Variety 



Fruits with a low 
seed value 



Fruits with a high 
seed value 



Number 
of spurs 



Average 

weight 
of spurs 

(grams) 



Number 
of spurs 



Average 
weight 
of spurs 
(grams) 



Baldwin 

Falla water .... 
Rhode Island . . 
Tompkins King 



12 

7 

8 

12 

6 

17 



3 
3 
5 
5 
9 
16 
[6 



Westfield 

All varieties 



138 



9 

4 

14 

9 

4 



1.80 
2.30 
2.03 
2. 10 
2.18 



3 24 



2 


2 .24 


3 


3 29 


3 


2 .00 


3 


2.08 


5 


3.01 





1.44 





2.25 



1 .64 



65 



2.07 



A poorly fertilized flower can develop into a fruit, provided it is borne 
on a vigorous spur; a weak spur, on the other hand, will mature only 
a fruit that is developing many good seeds. 

These data suggest that there is greater need for cross-pollination 
when the flowers are produced on trees growing under conditions that are 
unfavorable for the production of strong spurs, than for trees under 
favorable conditions. It is well known that apple trees growing in sod 
will usually produce less fruit than similar trees growing under cultiva- 
tion. Do sod trees produce less vigorous spurs than cultivated trees, 
and consequently demand better fertilization of the flowers to insure a 
set of fruit ? 

The following observations may throw some light on this question. A 
large number of apples from a mature Tompkins King tree growing in sod 
contained an average of 6. 1 seeds. Fruits from a tree of the same age and 
variety growing in a cultivated orchard had an average of 3.8 seeds. The 
orchards in question were about half a mile apart. In both, the oppor- 
tunities for cross-pollination were good. It seems reasonable to suppose 



Abscission of Flowers and Fruits of the Apple 



95 



that the apples which dropped from the trees in the sod orchard con- 
tained more seeds to the fruit than the drops from the well-cared-for trees. 
In other words, the former trees required the stimulus of many seeds to 
set fruit, while the latter set fruit even tho few seeds were developed. 

observations concerning some of the physiological effects of 

seeds 

It has been shown that the size of the fruits borne on a given branch 
under certain external conditions is dependent on the vigor of the spur 
and the seed value. The higher the seed value, the larger is the apple 
under conditions otherwise similar. This suggests that the seeds exert 
some influence which increases the supply of sap to the fruit in which 
they are borne. 

The heavier and more vigorous spurs, as previously shown, are pro- 
vided with a large diameter of conducting tissue, which permits of more 
abundant sap flow. Large spurs that have good conducting tissue are 
able to set fruit with a low seed value, whereas the fruits on the smaller 
spurs must have a high seed value if they are to continue development. 
One might assume that the handicap of poor conducting tissue in the 
small spur is overcome by the pull on the sap flow exerted by the seeds.' 
Small spurs require considerable help in order to provide an adequate 
supply of sap for a developing fruit, while large spurs need relatively 
little help. The following direct evidence is presented to show that many- 
seeded fruits actually do exert a greater pull on the sap flow than do 
few-seeded fruits. 

Withdrawal of water by leaves from fruits with varying numbers of seeds 

A number of spurs, each bearing one fruit, were taken from a branch 
of a Tompkins King tree in July, 1915. All but three of the leaves were 
removed from each spur, the leaves remaining being approximately of 
the same size and therefore the leaf surface on one spur being equal to 
that on any other. The fruits were coated with melted paraffin to pre- 
vent transpiration, and the spurs were then exposed in the laboratory. 
Some spurs without fruit and some detached fruits were exposed at the 
same time. 

In conformity with the observations of Chandler (19 14), the leaves on 
spurs that bore fruit remained turgid for several days, while the fruits 
on such spurs wilted and became shriveled. The leaves on spurs without 
fruit soon became dry and crisp. The detached fruits remained firm. That 
the leaves on the spurs bearing apples obtained their moisture from the 
fruit, is obvious. The point which is of special interest in this connection 



96 



Bulletin 393 



is that even tho the fruits were equally large in all cases, and even tho the 
leaf area was approximately the same on all spurs, some fruits remained 
firmer than others. The leaves on the spurs having the firm fruits dried 
before those on the spurs bearing the shriveled fruits. Examination 
showed that the badly shriveled fruits had fewer seeds than those which 
were comparatively firm. The greater the number of seeds, the less water 
was withdrawn from the fruit by the leaves. 

In several cases the fruit had not shriveled uniformly, but one side 
remained firm while the other was decidedly wrinkled. In most cases 
of this nature, the shriveled side corresponded to a seedless cavity while 
the firm side usually contained two seeds in the corresponding cavity 
(fig. 6). Similar results were obtained in repeated experiments, altho 
exceptions to the general rule were occasionally found. Such exceptions 





Fig. 6. cross sections of apples, showing the relation between 
seeds and the ability to withhold water 

The dotted area indicates the wilted part. It is associated with the seedless cavities 

might be explained on the basis of seed value. In these experiments 
it is essential to choose spurs that bear fruit under exactly similar con- 
ditions, as is emphasized later. 



Depression of freezing point by sap from fruits with varying numbers of 

seeds 

As Chandler (1913) has shown, sap obtained from leaves freezes at 
a lower temperature than sap obtained from green fruit. The movement 
of sap from fruit to leaves is accounted for by osmosis. Since leaves 
withdraw water from many-seeded fruits less rapidly than from few- 
seeded fruits, one might expect that the sap from fruits with many good 
seeds would depress the freezing point more than sap from few-seeded 
fruits. 

A few preliminary determinations regarding this point were made in 
August, 191 5. The results obtained are very suggestive. The sap was 



Abscission of Flowers and Fruits of the Apple 



97 



expressed from apples whose seed content was known. A single apple 
did not yield sufficient sap, hence three or four fruits with the same num- 
ber of seeds were used in each case. The apples were first ground up 
in a food chopper, and the sap was then expressed from the pomace. 
The freezing points of this sap were obtained by means of a Beckman 
apparatus. The results are given in table 47, which shows that the sap 
from fruits with few seeds depresses the freezing point less than does 
the sap from many-seeded fruits. It should be pointed out, in this con- 
nection, that these freezing points are for sap expressed from the live 
tissue of the fruits. If the tissue had been frozen before the sap was 
expressed the depression of the freezing point would no doubt have been 
greater in each case. 



TABLE 47. 



Depression of Freezing Point by Sap from Fruits with Varying 
Numbers of Seeds 



Variety 



Sap from fruits with 
few seeds 



Number 
of seeds 
in fruit 



Depression 

of freezing 

point 

(degrees 

centigrade) 



Sap from fruits with 
many seeds 



Number 
of seeds 
in fruit 



Depression 

of freezing 

point 

(degrees 

centigrade) 



Tompkins King 

Baldwin 

Westfield 

Fallawater .... 

Baldwin 

Rhode Island. . 

Average. . . 



1. 081 
1. 123 
0.972 
1 .009 
0.809 
0.900 



1 . 119 

1 153 
1 .024 
1 .027 
0.909 
0.967 



0.982 



6.2 



1 033 



The average weight of the spurs and of the fruits is given, in con- 
nection with the number of seeds and the depression of the freezing point, 
in table 48. These data likewise indicate that the sap of many -seeded 
fruits is capable of developing a greater osmotic pressure than the sap 
from few-seeded fruits. This fact suggests why the many-seeded fruits 
do not lose water as readily as do the few-seeded fruits. 

That the term greater seed value is more nearly accurate than many 
seeds is indicated by the last experiment in table 48. The eight-seeded 
fruits in this case have a lower seed value than the three-seeded fruits. 
As would be expected under such conditions, the three-seeded fruits show 
the greater sap density. 



Bulletin 393 



TABLE 48. Depression of Freezing Point by Sap from Fruits with Varying 
Numbers of Seeds, Weights of Spurs, and Weights of Fruits 



Lot 


• Average 
weight 
of spurs 
(gramsi 


Average 

weight 
of fruit 
•(grams) 


Num- 
ber of 
seeds 


Depression 

of freezing 

point 

(degrees 

centigrade) 


1 


5-47 
2. 11 

5-12 
2.31 

4.21 
4-32 


68.35 

68.53 

86 . 40 
51 24 

26.29 
25.62 


3 
5 

4 
5 

3 

8 


1 . 1 12 


2 


1. 152 
1 . 112 


7. 


1. 182 
0.900 




0.867 



Relation between formation of seeds and symmetrical development of fruit 
It may be of interest in this connection to record observations regarding 
the symmetry of fruits. Muller-Thurgau and Ewert give figures in which 
the amount of flesh of the fruit is more or less proportional to its seed 
content. If the seeds are confined to one side of an apple, only that 
side will be fully developed while the other side will be much smaller. 
Such unsymmetrical development is found in a high proportion of the 
fruits that are lost during the June drop. Comparatively few of the normal 
apples — those free from insect, disease, and other blemishes — ■ which 
remain on the tree are one-sided, altho mature fruits with one or more 
of their cavities seedless are frequently found. These observations can 
be explained in the following manner: 

As has just been shown, fruits with many seeds, or with a high seed 
value, apparently have denser sap than few-seeded fruits. Such many- 
seeded fruits can therefore exert a greater pull on the sap flow. If the 
fruit is bonie on a weak spur, the seeds play a very important part in 
obtaining sufficient food and water because the sap must pass thru a 
poorly developed conducting tissue. If a fruit with a seedless cavity 
happens to develop on a weak spur, the side without seeds suffers first 
and falls behind in growth. Sooner or later the poorly pollinated fruit 
on the weak spur drops, and hence many of the drops are one-sided. 
Poorly pollinated fruit that remains on the tree is usually borne on 
vigorous spurs. Such spurs are generally provided with good conducting 
tissue which can supply abundant sap with comparatively little stimu- 
lation such as is afforded by seeds. The influence of the seeds in fruits 
developed on strong spurs is therefore only a secondary influence, and 



Abscission of Flowers and Fruits of the Apple 



99 



the presence or absence of seeds in one cavity of the fruit makes relatively 
little difference in the growth of the corresponding side of the apple 






Fig. 7. CROSS SECTIONS of apples that dropped and of those that remained 

ON THE TREE 

The circles surrounding each section are drawn with the longest possible radius extending from the 
center of the core to the surface. The smaller apples are the June drops. In these the fruits fall behind in 
their development on the seedless side. In the apples remaining on the tree (the larger sections) asymmetry 
is not so closely correlated with the seedless cavity 

(fig. 7). Fruits remaining on weak spurs after the June drop are nor- 
mally well pollinated and generally develop seeds in all cavities; hence 
they too will be symmetrical. 



relations to be considered in choosing fruits borne under similar 

conditions 

As pointed out previously, it is very essential that fruits intended 
for study of the relations between size of fruit, number of seeds, and 
vigor of spur should be produced under exactly similar conditions. 
The following paragraphs suggest some of the things which must be kept 
in mind in choosing fruits suitable for this purpose. 



IOO 



Bulletin 393 



Position of the fruit on the spur, and number of seeds to the fruit 

The average apple spur bears five flowers. The central flower has the 
shortest stem and is usually the first to open in spring. In 191 5 at the 
station orchard, practically all the fruits that developed came from central 
flowers; fruits from lateral flowers with long stems were exceptional. 
In 19 1 6, on the other hand, comparatively few of the fruits had short 
stems. The reason for this is suggested by the following data, which 
were obtained just when the central flowers of the clusters were opening. 
The percentages are based on a consideration of all flower-bearing spurs 
borne on four large branches. There were over two hundred spurs. 

Percentage of spurs apparently normal 16 

Percentage of spurs with central flower abortive 58 

Percentage of spurs with stamens and styles of central flower abnormal . 26 

The abnormal stamens were undersized, malformed, and whitish; 
the styles also were malformed and dwarfed. The leaves of the spurs 
producing abnormal central flowers were somewhat wrinkled when they 
first opened. No disease and no insects were present. For a time it 
was believed that the injury might have been due to the dormant spray 
which was applied after the leaves appeared, but unsprayed trees along 
the roadside showed the same injury as did sprayed trees. These 
abnormalities were probably due to winter injury, presumably caused by 
a severe cold spell during early spring. The injury was not confined 
to any one variety, but all trees examined showed the same conditions. 
If the central flower was missing, the lateral flowers on the spur had 
longer stems than normal. 

Counts of the number of seeds in the fruits indicated that the number 
was higher in 19 16 than in 1915. This may have been due partly to the 
somewhat better weather during blooming time in 19 16 than in 191 5. 
The data in table 49 suggest that the position of the fruit on the spur 
may afford another explanation for this observation. It is seen from these 



TABLE 49. Number of Seeds in Short-stemmed and in Long-stemmed Fruit 



Variety 


Relative 
length 
of stem 


Number 

of 

fruits 


Average 
number 
of seeds 


Percentage 

with less 

than five 

seeds 


Tompkins King 

Baldwin 


Short .... 

Short .... 
Long 


50 
50 

50 
50 


5-58 
6.20 

5-38 
6.04 


32 
8 

32 
14 








Abscission of Flowers and Fruits of the Apple ioi 

figures that the short-stemmed fruits, which are developed from the 
central flower on the spurs, can set with fewer seeds than are needed for 
long-stemmed fruits which are developed from lateral flowers. 

Seed content and weights of long-stemmed and of short-stemmed fruits pro- 
duced on the same spur 

Casual observations indicated that frequently the weights of fruits 
borne on the same spur were not in proportion to their seed content; in 
many cases the fruits were of the same size altho the seed number varied, 
and in not a few cases the fruits with the smaller number of seeds were 
larger than the fruits with the greater number of seeds. Further study 
showed that the fruits which attained the larger size with the fewer seeds 
were the short-stemmed fruits. Representative data are given in table 50: 



TABLE 50. 



Seed Content and Weights of Long-stemmed and of Short- 
stemmed Fruits Borne on the Same Spur 





Long-stemmed fruits 


Short-stemmed fruits 


Spur 


Length 
of stem 
(milli- 
meters) 


Num- 
ber of 
seeds 


Weight 
of fruit 
(grams) 


Length 
of stem 
(milli- 
meters) 


Num- 
ber of 
seeds ■ 


Weight 
of fruit 
(grams) 


1 


24 
25 
21 

19 
24 


8 
6 
5 
7 
6 


27.0 
11 .0 
20.0 
19 5 
21-5 


16 
18 

2\ 
10 
14 


4 
6 
6 
4 
4 


29 
14 
22 


2 


3 


4. 


25 
24 


5. 




Average . . 


22.6 


6.4 


19.8 


15.8 


4.8 


22.8 







As has been mentioned, the short-stemmed fruit develops from the 
central flower, which is the first to open in spring. These flowers would 
probably be pollinated before the others, and it is possible that priority 
of pollination may be an advantage in causing a set with fewer seeds. 

The short stems frequently become clubbed, or fleshy (fig. 8). The cen- 
tral fruits are obviously in the most desirable position from the stand- 
point of sap supply. The fact that short-stemmed fruits can attain a 
larger size with fewer seeds than long-stemmed fruits on the same spur, 
lends further support to the theory that abundant sap flow is essential 
for fruit setting. Seeds are of value since they stimulate sap flow, but 
the size of the conducting tissue leading to the fruit is of considerable 
importance as well. This fact also emphasizes the importance of having 



102 Bulletin 393 

fruits borne under exactly the same conditions when studying the rela- 
tions between weight of fruit, vigor of spur, and number of seeds. Only 
fruits that have developed from flowers having a similar position on their 
respective spurs can be compared. 




Fig. 8. fruits with long and with short stems 

If a fruit with a long stem and one with a short stem are borne on the same spur, the former will usually 
be smaller than the latter even tho the former contains the greater number of seeds 

Relation between number of seeds and size of fruits on spurs bearing one 
and on those bearing two fruits 

In order to have fruits that are borne under the same conditions, only 
spurs bearing one fruit can be considered. If two fruits are borne on the 
same spur, the apples are developing under a handicap as compared with 
fruits borne singly. Data indicating that such conditions obtain are 
presented in table 51. Only the largest fruits on the two-fruited spurs 
were considered. The fruits were developed from lateral flowers on the 
spur. The variety was Tompkins King. It is seen from the table that 



Abscission of Flowers and Fruits of the Apple 103 

TABLE 51. Weight of Spur, Number of Seeds, and Weight of Fruit, 
on One-fruited and on Two-fruited Spurs 



Number of fruits to the spur 


Number 

of 

spurs 


Average 
weight 

of spurs 
(grams) 


Average 
number 
of seeds 


Average 
weight 
of fruit 
(grams) 


1 


50 
50 


2 .04 
2-43 


564 
6.86 


8.50 
8 81 


2 







the spurs bearing one fruit produce apples nearly as heavy as the more 
vigorous spurs with two fruits, even tho the latter have more seeds. 



Relation between aphid work and fruit development 
Number of seeds in normal apples and in apples stung by aphids. — 
Another influence causing unequal conditions among fruits otherwise 
similar is that exerted by the sting of the aphid. Apples severely injured 
by aphids are easily recognized by their malformed condition (Parrott, 
Hodgkiss, and Lathrop, 19 16). Such fruits will not drop even tho few 
or no seeds have been formed. Data regarding this point are given in 
table 52: 



TABLE 52. 



Average Number of Seeds in Normal Apples and in Apples 
Stung by Aphids 



Condition of fruit 


Number 
of 

fruits 


Average 
number 
of seeds 


Percentage 

having 

less than 

four seeds 


Percentage 
having 
no seeds 


Normal 

Stung by aphids 


50 
100 


6.94 
2 93 


22 

87 



20 







In many cases the injury caused by aphids is not very noticeable, 
especially after the fruit has attained a diameter of several centimeters. 
There is no conspicuous malformation of the apple, and the spurs are 
apparently free from the pest. On close examination, however, many 
fruits apparently normal show the effects of aphid work. Such fruits 
are frequently found on weak spurs in spite of a low seed value. The 
stimulation resulting from the attacks of the aphid may be held account- 
able for such apparent discrepancies. 

Water-core as affected by aphid work and water supply. — An observation 
regarding another influence of aphid work may be recorded at this time, 
since it shows that the aphid actually does influence the physiological 



T04 Bulletin 393 

activities of the fruit. In the early summer of 191 6, water-core was 
noticeable on a number of apples, especially Fall Pippin and Tompkins 
King. All the water-cored apples from several trees were closely examined, 
artd in every case observed such fruits had been stung by aphids. Not 
all the fruits injured by the lice were water-cored, but water-cored apples 
that had not been stung could not be found at that time. 

That water-core may, however, result from other conditions besides 
aphid work is shown by the following observations: During the early 
summer of 191 5, when the fruits were about three centimeters in diameter, 
a number of slender branches heavily laden with apples and leaves were 
cut from a tree and taken to the laboratory. The cut ends of the branches 
were placed in beakers containing water. Many of the fruits were removed, 
weighed, and cut open that same evening; none of these were water- 
logged. The next day all the apples from several different branches 
showed a water-cored condition. On the following day some fruits were 
again examined, all of which were found to be normal. Similar observa- 
tions were subsequently made on twigs brought into the laboratory pri- 
marily for this purpose. 

These facts can be accounted for by the following probable explanation : 
The ends of the freshly cut twigs permitted the free passage of water 
into the branch. Transpiration during the night was reduced to a mini- 
mum, which resulted in the accumulation of water in the fruit, thereby 
producing the water-logged condition. After some time the ends of the 
twigs became clogged, due to bacterial development, and as a result water 
entered less freely. The leaves transpired water more rapidly than it 
could be supplied thru the cut end of the twigs. This produced con- 
ditions favoring incipient drying, and hence the leaves began to with- 
draw water from the fruit. After the withdrawal of water had been going 
on for a time, the fruit regained its normal condition. 

The water-cored condition observed in connection with aphid work 
cannot be changed by detaching the spur and allowing the leaves to with- 
draw the water. The leaves on detached spurs with aphid-stung fruit 
that was water-cored, dried up in all cases, while the fruit itself remained 
firm. Do apples injured by lice develop a greater sap concentration than 
they normally possess? Unfortunately no determinations were made 
regarding this question. 

EXPERIMENTS CONCERNING THE ABSCISS-LAYER 

The shedding of flowers and immature fruits is brought about by the 
formation of an absciss-layer similar to that which precedes leaf fall 



Abscission of Flowers and Fruits of the Apple 105 

(Pfeffer, 1904). The formation of such a layer was induced by the follow- 
ing means: (1) removing the fruit and leaving varying lengths of stem; 
(2) coating the fruit with vaseline; and (3) submitting the fruit to humid 
atmospheric conditions. The effects of these various treatments are 
given below. 

The observations recorded suggest that the formation of the absciss- 
layer is associated with the inhibition of sap movement. So long as the 
sap passes into the fruit, .as it does under normal conditions, or away from 
it as is the case when the leaves draw the watery sap from the fruit, the 
layer is not formed ; but when the movement of sap ceases while the spur 
is still active, as it does when the fruit is removed from the stem or when 
transpiration is checked by coating the fruit with vaseline or by exposing 
the fruit and the spur to humid conditions, the absciss-layer is produced 
which brings about the shedding of the fruit or the stem. 

Effect of removing fruit and leaving varying lengths of stem 
A number of Maiden Blush fruits ranging from one to one and one-half 
centimeters in diameter were cut from the stems in such a way that the 
stem in each case remained attached to the spur. The length of the 
stems remaining after the removal of the fruits varied. In some cases 
the fruit was removed and the entire stem was allowed to remain on the 
spur; in other cases the stem was shortened to half its original length. 
The first experiment was performed on June 8, 19 15. Six days later the 
short stems readily snapped from the spurs when touched and the long 
stems adhered somewhat firmly, while stems that had fruits did not come 
off when touched. Two days later the long stems from which the fruits 
had been removed fell naturally. Repeated experiments gave similar 
results. Removal of the fruit from the stem induced the formation of 
the absciss-layer which resulted in the shedding of the stem. The shorter 
the stem, the more quickly, apparently, was this layer formed. 

Effect of coating fruit with vaseline 
In connection with studies concerning aphid work, the entire fruit, 
stem and all, was coated with vaseline. All fruits so treated fell within 
a week, while uncoated apples remained attached. Subsequent experi- 
ments regarding the influence of coating the fruit with vaseline gave 
similar results. The same effect was obtained by coating the fruit with 
grafting wax. The treated apples were apparently normal in all respects. 
The effects of coating would be to inhibit transpiration and exchange 
of gases. 



106 Bulletin 393 

Effect of slow and of rapid drying of leaves on detached spurs with 
uncoated fruit and on detached spurs with vaseline-coated fruit. — Spurs with 
leaves and fruits were taken from the orchard and put in the laboratory. 
About half of the fruits were coated with vaseline, while the others were 
left untreated. Some spurs with the fruits coated and some with 
uncoated fruits were exposed in the laboratory with the cut ends in 
water; others of each lot were exposed in the same place but without hav- 
ing access to water. 

After eight days the leaves on the spurs with their cut ends in water 
were green and turgid. The vaseline-coated fruits had all fallen from 
these spurs, while the uncoated fruits remained attached. In both cases 
the fruits were fully turgid. The leaves on spurs not having access to 
water were dried up and the fruits were shriveled, but both the vaseline- 
coated and the normal fruits remained attached. 

Effect of a saturated and of a dry atmosphere on abscission of fruit on 

detached spurs 

A number of spurs with leaves and fruits were brought into the labora- 
tory and placed in a heavy paper sack, after which they were thoroly 
moistened by immersing them in water and then allowing the water to drain 
off thru perforations in the bag. They were given the same treatment every 
day for a week. Another lot of spurs was obtained at the same time, but 
they were accidentally overlooked when the others were moistened. 
At the end of the week, the spurs in the bag that had been moistened 
every day had lost all their fruit; the leaves were turgid and green, and 
remained attached to the spurs. The spurs that had not been moistened 
had lost all their leaves, which were yellow and crisp, but the fruit re- 
mained attached to the spur. The fruits in the humid atmosphere of the 
moistened bag remained firm, while those in the dry bag had shriveled. 
Similar observations were subsequently made. 

SUMMARY 

The facts and observations contained in the foregoing pages may be 
summarized as follows: 

1. From two-fifths to four-fifths of the total number of flowers are 
lost during the early drop. 

2. In some varieties practically all flower-bearing spurs set fruit after 
the first drop; in others almost half of the spurs fail to develop fruits. 

3. The proportion of spurs that set fruit after the first drop varies 
considerably on different trees of the same variety and on different limbs 
of the same tree. 



Abscission of Flowers and Fruits of the Apple 107 

4. Only three to seven per cent of the total number of flowers finally 
develop into fruits. 

5. If comparatively few flowers begin to develop fruits, the June drop 
will be small ; if a large number of flowers begin development, the June 
drop will be heavy. 

6. From one-sixth to one-third of the flower-bearing spurs finally set 
fruit. 

7. The proportion of spurs that hold fruit after the June drop varies 
in different trees of the same variety and on different limbs of the same 
tree. These variations are not due entirely to the location of the limb 
or to the angle at which it grows. 

8. A larger proportion of spurs set fruit on limbs that have produced 
a relatively light bloom than on limbs that have produced a full bloom. 

9. Spurs on limbs with large leaves are more likely to set fruit than 
spurs on limbs with small leaves. 

10. During 191 5 there was no consistent difference in fruitfulness 
between the spurs arising from 19 13 wood and those arising from older 
wood. Comparatively few spurs arising from lateral buds on 19 14 wood 
set fruit in 19 15. The shorter the terminal growth during 19 14, the 
greater was the tendency for lateral buds to set fruit in 191 5. 

11. The spurs occurring near the end of a season's growth, or just 
before a zone of weak buds, are the most likely to set fruit. As a rule, 
the spurs in the terminal half of a given season's growth set more 
abundantly than spurs in the basal part. 

12. Spurs that lose all flowers and fruits during the first drop average 
fewer flowers to the spur than those that hold fruit after the June drop. 

13. Spurs producing many flowers are more likely to set fruit than 
those that produce a small number of flowers. 

14. A higher proportion of the flowers produced on spurs with many 
flowers set fruit, than is the case with spurs producing few flowers. 

15. Spurs making more than one centimeter of growth during the 
preceding season have a greater tendency to set fruit than those that 
make less than one centimeter of growth. 

16. Spurs that finally set fruit are heavier than those that lose all their 
flowers and fruits. Those that hold fruit until the June drop are heavier 
than those that lose their flowers during the first drop. 

17. Spurs bearing two fruits weigh more than those bearing only one 
fruit. 

18. A larger proportion of strong spurs set two fruits to the spur than 
is the case with weak spurs. 

19. Spurs which produce many flowers are heavier than spurs which 
are taken from the same limb but which produce few flowers. 



108 Bulletin 393 

20. Spurs arising from buds that are terminal on a spur growth of 
more than one centimeter have a greater average weight than spurs 
from buds borne at the end of a shorter growth. 

21. The cylinders of conducting tissue have a greater diameter in 
the heavy spurs than in the light spurs. 

22. The average weight of spurs on limbs that produce few flower- 
bearing spurs is greater than for spurs produced on limbs with a full 
bloom. Spurs with a given diameter on the former limbs weigh more 
than spurs with the same diameter from the limbs with a full bloom. 

23. The water supply is a factor in increasing the size of leaves. More 
water passes to vigorous buds than to weak buds. 

24. Frequently the spurs that set fruit make a vigorous lateral growth. 
Limbs that set fruit on a high proportion of spurs often produce the 
largest amount of lateral growth from flower-bearing spurs. 

25. Limbs receiving a diminished supply of sap produce fewer fruits 
to a hundred spurs than limbs receiving a normal or an excessive supply 
of sap. The small spurs as well as the large ones are benefited by an 
increased amount of sap. 

26. Vigorous spurs from which all the leaves are removed before the 
flower buds open are not so fruitful as similar spurs that are not defoliated. 
Vigorous spurs that have all but two leaves removed, set approximately 
as well as normal spurs, which usually have from seven to ten bud leaves. 
The proportion of spurs setting more than one fruit is three times as 
great in the case of the check spurs as in the defoliated lot. 

27. Spurs inclosed in white translucent sacks are more fruitful than 
those inclosed in brown opaque sacks. 

28. The apples that fall in the early stages of their development have 
fewer seeds, on the average, than the apples that remain on the tree; but 
many fruits remaining on the tree have few seeds, and many fruits that 
drop have a high seed content. 

29. In general, the weight of the fruit is proportional to the number 
of seeds in the fruit. The vigor of the spur on which the fruit is borne, 
and the size of the embryos in the seeds contained in the apple, also play 
a part in determining the weight of the fruit. The term seed value 
emphasizes the quality of the seeds. This quality is manifested by the 
ability of the individual seeds to increase the weight of the fruit, and it is 
associated with the size of the embryo contained in the seed. The quality 
may be the result of cross-fertilization. 

30. Spurs bearing fruit with a low seed value are heavier on the average 
than spurs produced on the same limb but bearing fruits with a high 
seed value. 



Abscission of Flowers and Fruits of the Apple 109 

31. Leaves on detached spurs that bear fruit remain turgid for some 
time, since they can draw water from the fruit. Apples with many- 
seeds lose less water than those with few seeds. 

32. Sap from fruit with few seeds depresses the freezing point less 
than does sap from many-seeded fruits. 

33. Unsymmetrical fruits resulting from imperfect fertilization are 
more frequent in fruit that has dropped than in fruit that remains on 
the tree. 

34. Short-stemmed fruits, which are developed from central flowers, 
have fewer seeds on the average than do long-stemmed fruits. 

35. Fruits with short stems usually attain a greater weight than fruits 
with long stems borne on the same spur, even tho the latter may contain 
more seeds. 

36. Fruits borne singly on vigorous spurs may attain a weight as great 
as that of the larger apples from spurs bearing two fruits, even tho the 
latter may have a greater seed content. 

37. The average number of seeds in a normal apple is greater than 
in fruit that has been stung by aphids. Apples attacked by aphids remain 
attached to the tree even tho no seeds are formed. 

38. Fruits stung by aphids may develop a water-cored condition. 
Such a condition is also caused by over-abundant water supply. 

39. Removal of the fruit from its stem induces the formation of an 
absciss-layer between the stem and the spur, which results in the shedding 
of the stem. The shorter the stem, the more quickly is the absciss-layer 
formed. 

40. Fruits coated with vaseline or grafting wax fall after one week. 

41. Detached fruiting spurs kept in a receptacle with a saturated 
atmosphere lose their apples after several days; similar spurs kept in 
a dry atmosphere retain their fruit. 

42. Vaseline-coated fruits on spurs with their stems standing in water 
fall after eight days; fruits similarly treated on spurs not having access 
to water remain attached to the spurs. Untreated fruits on spurs standing 
in water also remain hanging. 

general discussion 

The results presented in the foregoing pages emphasize the importance 
of vigor, more especially the vigor of the individual spur, as a factor 
in fruit setting. As compared to weak spurs, the previous season's growth 
of vigorous spurs is longer, the new spur growth is heavier, the leaves 
are larger and more numerous, there are more flowers to the spur, the 
diameter of the conducting tissue is greater, and the weight of the lateral 
spur growth is greater. 



no Bulletin 393 

The vigorous spurs seem to favor fruit setting because they can supply 
the developing fruits with an abundance of water and food. Seeds appear 
to be valuable because they supplement the forces that bring sap to the 
fruit. Strong seeds are of primary importance for the setting of fruit 
on relatively weak spurs; they are of lesser importance for the setting 
of fruit on strong spurs. 

The number of strong seeds is dependent on effective fertilization, 
which in turn presupposes cross-pollination. Even tho the grower may 
plant several varieties of the same fruit which bloom during the same 
time, nevertheless cross-pollination is frequently prevented by unfavorable 
weather during blooming time. Man has little control over the weather. 
On the other hand, man may influence the vigor of the tree by cultural 
methods. Trees in sod, for example, are usually less vigorous than trees 
in a tilled orchard. The latter, as a rule, produce heavier crops of fruit. 

In Mr. Cornwall's orchard, at Pultneyville, New York, the Baldwin 
trees were heavily laden with fruit in 1915. Other Baldwin trees around 
Pultneyville produced relatively light crops that year. The weather 
at blooming time in that locality was cold, cloudy, windy, and rainy — 
very unfavorable for cross-pollination. The trees on the Cornwall farm 
were in the best of condition. The owner plowed his orchard very early 
in the spring and put in a cover crop the latter part of June and early 
in July. This treatment would be conducive to rapid, vigorous growth 
of the spurs early in spring, and early planting of the cover crop would 
tend to check further elongation and permit of abundant food storage 
in and near the terminal buds. According to the observations recorded 
herein, such conditions would favor fruit setting without the aid of many 
strong seeds, and hence a fairly good crop might be expected even tho the 
weather during blooming time were unfavorable. Plowing in late fall 
under some conditions may prove more advantageous than very late 
spring plowing, so far as setting of fruit is concerned. 

The application of a quick-acting nitrogenous fertilizer, such as sodium 
nitrate, early in spring may have a decided effect in stimulating early 
and rapid spur growth that would be likely to set fruit the following 
year. Some evidence for this suggestion is contained in the paper by 
Lewis and Allen (191 5), received by the writer while the present report 
was in the course of preparation. 

Much has been said regarding so-called self-sterility of certain varieties 
which under a given set of conditions seem to be benefited by cross- 
pollination. As has been observed by Waite (1894) and others, the 
degree of self-sterility varies from year to year and in different trees 
of the same variety under different cultural treatments and in different 
localities. From the standpoint of the species, a condition of self-sterility 



Abscission of Flowers and Fruits of the Apple hi 

is desirable because only cross-pollinated flowers would mature fruits 
and seeds on such trees. Cross-pollinated seeds would tend to produce 
more variable seedlings, and it might be expected that desirable variations, 
from the species' standpoint, would occur. 

From man's standpoint, however, self -fertile varieties, or those that 
can mature fruit without strong seeds, are more desirable because there 
are more chances of a crop if the necessity of cross-pollination can be 
eliminated. So far as is known in the case of the apple, the presence 
of seeds has no effect on the quality of the fruit. Seeds affect the size, 
but size can be produced without the aid of seeds. It is conceivable 
that a tree bearing a heavy crop of many -seeded fruits is being devitalized 
to a far greater extent than another tree of the same variety bearing a 
crop of fruits equally heavy but having relatively few seeds. This hypoth- 
esis presupposes that the production of seeds requires more energy and 
food than the mere production of the flesh of the fruit. 

The problem, then, it seems, is to find cultural treatments that are 
favorable to self-fertility. This is by no means a simple problem. One 
should not expect, for example, that the soil treatment which proves 
favorable for one or more varieties will prove favorable for all. Any 
treatments, however, that produce relatively long spur growth and provide 
for an abundance of stored food, and any treatments that influence the 
vigor of the individual spur, may be expected to be favorable for the 
development of blossoms into fruit without cross-pollination. Unfavorable 
climatic conditions may be involved in the self -sterility of a given variety ; 
if such is the case, nothing can be done but to make the best provisions 
for cross-pollination. 

The observations and experiments recorded in the preceding pages 
justify the tentative conclusion that unfavorable conditions of nutrition 
and water supply are among the basic factors which cause the normal 
drop of flowers and partially developed fruits of the apple. All factors 
that have a direct or an indirect influence on nutrition and water supply 
of the flower and the fruit, such as pollination, weather, cultivation, 
and the like, are of importance. Fruit development, however, is possible 
without cross-pollination and even under relatively unfavorable weather 
conditions, so long as the young fruit has an abundant supply of water 
and of readily available food. 



Bulletin 393 



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